Words & illustrations by Andrew Emmerson

This is an 'entry level' guide to the subject, with links to resources on other websites.

Clicks and buzzes
What did people do before the speaking clock was invented if they wanted a time check?  Simple: they rang the operator and asked her the time by the exchange clock on the wall, but this was not precise to the second, nor could the exchange always answer just when the customer wanted.  The first genuine speaking clock machine was introduced in the USA in 1927, coming to Paris in 1933, The Hague in 1934 and Switzerland in 1935.  But automatic time service (of a Heath-Robinson kind) had been available to telephone users in San Francisco since the late 19th century; by listening for to an observatory clock at least a minute and decoding clicks and single and double buzzes against some detailed instructions you could set a pocket watch - but it helped if you already knew more or less what the time was.  A proper speaking clock is far more convenient...


Mark I

The first British clock
The Speaking Clock service was inaugurated in London on 24th July 1936 with a pair of clocks in Museum Telephone Exchange, Holborn (they had been developed by the Post Office Research Station at Dollis Hill, North London).  Distribution of the service is by means of relay sets installed in the Tandem Exchange which allows up to 100 simultaneous calls to be connected to the clock.

A second pair of clocks was installed at Lancaster House in Liverpool during 1942 as a safeguard against interruption, with a 'ring main' connecting both sets of clocks by diverse routes to all exchange centres in the country.

Speaking Clock showing glass discs
Picture dated 1936

Speaking Clock under test
Picture dated 1936

P4727 - the first speaking clock mechanism, which used photographic storage in revolving glass discs.
Holborn Exchange, London
Picture dated 1950

P1280 - a technician adjusts the amplifiers of the first speaking 
clock mechanism; note Telephone No. 121 and Bellset No. 20 on the wall at rear.
Picture dated 1936



P1281 - technician checking the speaking clock apparatus at Holborn Exchange
Picture dated 1936

Click here for more pictures of the Speaking Clock Mark I

Click here for an assembly drawing of the Speaking Clock Mk I

Here is a 'popular' description of TIM, taken from Practical Mechanics magazine, May 1938 (page 425)

A brief description of TIM the G.P.O. Clock, which has answered over 20,000,000 calls since its installation just over a year ago.

By William G. Pike

Talking Clocks are not new inventions, for clocks of this nature have been in use for a considerable time in Europe, Asia and elsewhere.  There is nothing, however, quite like TIM, the wonder instrument of the Post Office.  The sounds which come from this clock are recorded on glass discs, reproduction is remarkably clear and the discs are practically everlasting.  Eighteen months' severe testing in the Post Office research station has resulted in the clock giving an extremely accurate performance. It is only possible, at present, to hear this clock in the London district, but it is hoped to extend the service to other  large towns in the near future.  Proof of the popularity of this clock is shown by the fact that over 20,000,000 calls have been made since its installation a little more than a year ago.  The public's appreciation of accurate time is evident, for 37,000 people asked the time between 8 a.m. and zero hour on the last Armistice Day.

Glass Discs
The main part of this ingenious clock consists of four circular glass discs like gramophone records.  On each disc are photographed the various numbers and phrases as spoken into a special microphone by Miss J. Cain, who is now known as "the girl with the golden voice."  The sound tracks, similar to those on the edge of a talkie, film, are arranged in a series of concentric circles.

Upon dialling the letters TIM (code 846) a subscriber is connected with the clock and hears a voice repeating the time.  The announcement is phrased as follows: "At the third stroke it will be ten, twenty-five and thirty seconds precisely" (or whatever time it is) followed by pip ... pip ... pip.  The period of listening lasts from 1.5 minutes to 3 minutes, after which the call is automatically cut off.

Of the four discs, two share the minutes, each having thirty sound tracks. The other two discs are used for the hours and seconds. The hour disc has twelve tracks and the seconds disc six tracks. The various words of the sentences are also recorded on the various discs, so that when an announcement is made all the discs come into use.

Speech Reproduction
The reproduction if speech from the sound tracks is produced by focussing a ray of light on the discs and letting the light fall onto a photo-electric cell mounted on the opposite side. The electric current from the photo-cells is amplified, the volume of sound being such that two hundred people may listen at the same time.

The light rays are obtained from small electric lamps and a number of lenses. Each disc has its own lamp and set of lenses, usually referred to as the "scanners." The "scanners" are mounted on carriers which move in and out of the discs in order that the ray falls on the appropriate track. Movement of the "scanners" is governed by cams mounted on the carrier shaft. The cams work in conjunction with three ratchet wheels, one each for the hours, the minutes and the seconds, the ratchet mechanism being operated by trip magnets.

Extreme Accuracy
A very accurately controlled electric motor drives both the discs and the scanners.  Extreme accuracy is ensured, for the motor speed is governed by a master clock having a free pendulum, beating seconds.  Attached to the bottom of the pendulum is a slide having a number of transparent areas.  Placed in front of the slide is an electric lamp, a series of lenses and a narrow vertical slit, and behind the slide is a photo­cell.

The current produced by the light falling on the photo-cell is amplified and used to give impulse to the pendulum.  As long as the pendulum vibration. is constant, no impulse is given, but as soon as the vibration decreases, current from the photo-cell is used to increase the vibration to normal.  In order that the error between the third pip and true time shall not be more than 0.1 second, the master clock is connected by relays to Greenwich Observatory and synchronisation takes place every hour.  Should the clock be out of step with Greenwich time, one of a number of relays is operated, causing the current in the coil of a magnet - which is placed beneath an armature fixed to the pendulum rod - to vary.  By varying the force the rate of the pendulum can be advanced or retarded and brought into step

Two Clocks
Actually there are two clocks installed at the exchange.  Erected side by side, both are running continuously.  Should the first clock break down or have an error in excess of a tenth of a second from G.M.T. at any hour, the second clock automatically comes into action.  The Post Office have spared no energy to make this service the most accurate possible and they have been rewarded. TIM has already netted the sum of £85,000.

Full technical details of the Speaking Clock were given in a number of Journals.  Many of these can be viewed in the Downloads section at the bottom of this page.

P4728 - the room where the first speaking clock was installed
Holborn Exchange

Close up of the Speaking Clock Mk 1
Holborn Exchange


Inauguration of the Speaking Clock at Holborn
Picture dated 1935

Wartime developments
During World War II technology from the Speaking Clock was applied to other interesting projects.  Special noise-cancelling microphones and headphones were devised by the Post Office for tank use. Deep below their Dollis Hill research station a special chamber with deafening sound effects was constructed to simulate a tank's interior.  Producing the sound effects with which to test these devices was another matter; recordings on 78rpm gramophone records would not last long enough and the chosen solution made good use of other Post Office technology.

First of all recordings were made - on direct-cut disk - of a tank rumbling past a microphone.  Ten-second recordings made in this way were transferred to 35mm film by the Crown Film Unit (a new name for  the old Post Office Film Unit) and a two-second long section finally transferred to glass disc, for playing continuously on a speaking clock machine.

Apparently the joint in the recording and the two-second repetition were not noticeable in use. Similar machines were made for the Royal Air Force; these generated continuous background aircraft noise effects for training radio operators.  Four different aircraft types were covered, at normal speed and at absolute maximum.  Yet another machine was for training fighter pilots; this was a twin-channel simulator, providing continuous aircraft noise and spasmodic machine-gun effects as and when required.

Postwar developments
During the Cold War the speaking clock network was designed to be used in case of nuclear attack to broadcast messages from Strike Command at High Wycombe to regional police stations. 

From there, automatic warning sirens could be started and alerts sent to Royal Observer Corps monitoring posts.  The design used the existing Speaking Clock circuit that ran around the UK rather than a dedicated system.  This ensured that any break down in service would be noticed straight away. 

The signals to sirens were sent down the wires of individual subscribers for the same reason.  As customers would report any fault as soon as it occurred this ensured that the line would be repaired as soon as possible.

Mark 2

A Mark 2 clock, which was a replica of the Mark 1, using similar photographic soundtracks but with quartz crystal oscillators for greater accuracy was produced in 1954.

The accuracy of the new clocks was plus or minus 5ms when corrected hourly, whereas the Mark 1 clocks were plus or minus 100ms when corrected hourly.  The correction is automated in the mark 2.

Due to the new design with it's much improved accuracy, the Australian Postmaster General ordered clocks for Melbourne and Sydney.

These Mark 2 clocks can now be viewed in the National Communications Museum in Australia.

Mark II Rack Layout - EX89000

Mark II Schematic - EX28925

Mark II Room Layouts - EX28851

Mark II Assembly - EX43400

Mark 2 - Operated from 1954 to 1990 in the City West Exchange, Melbourne

Mark 2 clock installation

Posters advertising the Australian Speaking Clock service (1954)

The Post Office decided in the early 1960's that due to the London clocks requiring relocation and the deterioration of the clock wiring it would be best to renew the clocks and install them in their new location.

Mark 3

In 1963, the Mark 2 clocks were superseded by the Speaking Clock Mark 3, which used modern recording technology of a magnetic media.  This was a rotating metallic drum with a thick layer of magnetically loaded Neoprene and driven from a crystal controlled oscillator.  The crystals are maintained at a temperature of 50 degrees C in an oven.

The new London clocks were also installed in the Trunk North Control which had un-interrupted power and a much better working environment.  They came into service in October 1963 and the Liverpool clocks followed in October 1963.  In the interim period from May to October the prototype clock at the GPO Research Station at Dollis Hill acted as a standby to cover the London clocks which were serving the entire country.

Synchronisation also changed from Greenwich to Rugby.  This was now daily and the feed was by landline.

These Mark 3 clocks, using a revolving magnetic drum, replaced the original speaking clock introduced in 1936. The 79 separate phrases required for a 12-hour clock were recorded as circular tracks spaced 1/16 inch apart along the length of the drum. The pips were not recorded on the drum but were derived from an oscillator.  The Speaking Clock had accuracy to approximately 1/20 second.  Like the first clock, the second speaking clock had its accuracy calibrated and corrected by referencing to a time signal from the Royal Greenwich Observatory, broadcast by Rugby Radio Station.

Two clocks were installed, one in London and one in Liverpool and were joined together by the dedicated double ring-main trunk circuit that ran around England.  Under normal conditions one clock at each centre supplies approximately half the country, but under fault conditions either installation could take the full load.

The company that manufactured the rotating magnetic drum part of the Speaking Clock was Roberts & Armstrong (Engineers) Ltd of North Wembley. They took on the licence from the British Post Office to manufacture complete clocks for the telecommunications authorities of Denmark, Sweden and the Republic of Ireland, and a third (spare) clock for the British Post Office. The latter was installed in Bow Street, London. The European clocks were modified for the 24-hour system by lengthening the drum and adding extra heads. Roberts & Armstrong subcontracted the electronic aspects to the Synchronome Company of Westbury. The clocks were designed to run non-stop for 20 years.

Speaking Clock Mark 3

Speaking Clock Mark 3 - close up


Speaking Clock Mark 3 - control covers open
Picture taken in 1967 at Judd Street, London with Pat Simmons


Mark IV

In the 1980's British Telecom devised the Mark 4 which was a solid state speaking clock known as Chronocal.  It occupied a 19-inch rack cabinet about 3U (5.25") tall and based on the ACRE CP85 processor board.  It also included a radio receiver so that it could make use of the 60hz time correction signal, but still retained the Rugby landline for extra security.   

It went live in mid 1984 and could be equipped with either the Pat Simmons or Brian Cobby voices.  This system is solid state and has no moving parts at all.

During the 1980's (possibly 1990's) BT renamed the Speaking Clock 'Timeline' but the name did not find much appeal.

Since 2001, Time & Frequency Solutions have supplied the technology behind the Speaking Clock.  Teligent, the telecoms specialist, supplies the vital switching gear enabling multiple users to access the system at the same time.  The time source used is a Time & Frequency Solutions M211 Master Clock Timing System with a redundancy element to ensure continued working even if a fault developed.


20,000,000 calls to TIM in the first year - 1936.

265,000,000 calls to TIM from London users from 1936 - 1949.
400,000,000 calls to TIM nationwide from 1936 - 1949.
70 million calls to TIM nationwide in 2006.
30 million calls to TIM nationwide in 2011.


The people behind the voices


Final of Golden Voice Competition for the Speaking Clock



Postmaster General with judges who included Major Tryon and Mr John Masefield, the Poet Laureate
(Picture dated 21 June 1935)



Finalists of the Golden Voice competition (1935)



The voices of TIM

Jane Cane
he first voice of the Speaking Clock voice.  She was chosen after a nationwide competition among 15,000 women telephonists and was awarded ten guineas (£10.50).  Until then she used her first name Ethel but dropped this in favour of her middle name, Jane, and made a record for the GPO helping other staff improve their speaking voice.  She went on to become announcer for Henry Hall during one of his broadcast concerts and was offered a film part by Columbia Pictures under the name of Jane CainBorn 1st May 1909 - died aged 87 on 19th September 1996.

Ethel Cain recording the speaking clock in 1935

Miss Ethel Cain dialling TIM at Dollis Hill to hear her own voice tell the time, 20th March 1936


Radio and Television Exhibition, Earls Court, London
Picture taken 1960

Gordon Gow & Richard Peach
In 1953 Gordon Gow, a radio broadcaster and theatre critic, was the recording voice for the Mark 2 clocks that were exported to Australia.  Gordon was born in Australia and moved to London in the early 1950's.  He was commonly referred to as ‘George the talking clock’.

The original disks were replaced in 1958 with some recordings, not used in 1953, replacing phrases that were not to the satisfaction of the Australian Post Office.

Telstra, in 1990, replaced Gordon Gow's voice with that of Richard Peach, the ABC Broadcaster.

Gordon Gow (Picture dated 1953)

Richard Peach


Pat Simmons
A competition was held in 1963 to find a replacement for Miss Jane Cain's voice for the Mark 3 Speaking Clock.  It was won by Miss Pat Simmons, an Assistant Supervisor in Avenue Telephone Exchange, London.  She was to be heard until Brian Cobby replaced her in 1985.

Pat Simmons recording

Pat Simmons recording

Brian Cobby
Brian was the voice of the Speaking Clock from 1985 until 2007.

The voice of the Speaking Clock today, he was interviewed and this is an extract

How did you become the voice of the speaking clock?
I moved to Brighton more than 30 years ago and got a job with the Post Office, where I worked for 16 years.  In 1984, British Telecom [as the Post Office's telephone arm became in 1981] decided to change the speaking clock.  They ran a competition among the staff to find a replacement voice, which had to be clear and warm with no regional accent.  After a series of regional heats, I beat a lady from Lowestoft in the final.  She became the voice that says, "the number you have called has not been recognised." I became the voice of the speaking clock on 2 April 1985 at 11am, precisely.  The telephone lines were jammed with people trying to listen.

How long did the announcements take to record?
Just an hour, but it was hard work. I recorded the times in a studio in London, where I had to read from a 33-page script.  It was calculated mathematically [only 86 words are actually used], so I didn't have to go all the way round the clock.  Later, we found that we hadn't taped the 'o' clock' so I had to drive back up to London just to record that.

Might we have heard your voice anywhere else?

Maybe. Before I worked for BT I was an actor.  As well as films and some Shakespeare, I did a lot of voiceover work, mostly for commercials. In 1965, I did one of my most famous voiceovers: the countdown for the TV programme Thunderbirds.

The poster above them looks intriguing...

Yes, it's from a 1959 film I did, called The Nudist Story.  It was billed as being shown in 'blushing technicolor'. Many years later, a Sunday paper ran a story, 'Speaking clock in nude movie'.  The picture they printed of me was actually that of a boy who played my brother, who, alas, was a lot skinnier than me.  I had a great body in those days...

The wording of Brian Cobby's announcement was altered in 1986 to include the phrase "sponsored by Accurist " to become "At the third stroke the time sponsored by Accurist will be...."

Lenny Henry
Lenny Henry is to provide the voice of the speaking clock for the next fortnight.  The comic's Black Country burr will replace the usual plummy tones of BT's service as part of a Comic Relief fundraising drive.  Callers dialling 123 pay will 10p for the service, and proceeds from today to March 23 are expected to raise £200,000 for the charity.  Lenny, who is temporarily replacing Brian Cobby as the voice of the clock, is only the fourth ever person to take on the role in its 67-year history.  He will be putting on a different voice each day in the hope of encouraging people to ring back.  He said: "I can hardly believe it.  Wait until you hear what we've done to the pips." March 10, 2003

Alicia Roland
A 12-year-old girl says she is proud to have become the only child and the first Scot to record the Speaking Clock in its 67-year history.  The schoolgirl's voice will be heard by up to two million callers over the next week.  Alicia, from Brookfield, Renfrewshire, beat thousands of children from all over the UK in a competition to become the voice for a week.  The idea is part of the Big Listen, a week of activities which encourages adults to listen to young people and raise money for the charity ChildLine. Organisers estimate Alicia will raise £200,000 during her week in the job - calls cost 10p and BT is donating every penny to the good cause.  She said: "It's very nice to be the first child to do this job, I think it's good for people to hear a child's voice when they ring up. My friends at school were a wee bit envious but they've been really supportive, they said they're going to ring up the clock loads this week."   It is only the fifth time that the Speaking Clock - which began in 1936 and receives 80 million calls a year - has been changed. 13th October 2003

Sara Mendes da Costa
Born in 1966, Sara Mendes da Costa from Brighton became the fourth permanent voice of the UK Speaking Clock in 2007.

On 23th October 2006, to mark the BT clock reaching its 70th year, a competition was launched to find the new modern voice of the Speaking Clock.  Applicants were invited to leave telephone recordings of their voice, with the proceeds of each call going to Children in Need.  Sara Mendes da Costa, a telemarketer and part-time voiceover artist, was announced as the winner on BBC One's Children in Need telethon on 17th November 2006.

She was the unanimous choice of a voting panel that included the clock's previous voice, Brian Cobby, the BBC presenters Natasha Kaplinsky & Alan Dedicoat, and Sir Christopher Bland, chairman of BT Group.


Sport Relief 2012
For five weeks only, David Walliams joined Chris Moyles, Kimberley Walsh, Gary Barlow and Fearne Cotton as the voice of the BT Speaking Clock.  This was between Wednesday 7th March 2012 and Monday 9th April 2012.

To celebrate the new voice, BT ran a competition on its Facebook page giving fans a chance to win a limited edition David Walliams wall clock.  To enter you had to guess the mystery celebrity voice telling the time that day.  If you named correctly your name will automatically be placed in a daily prize draw to win the prize.


Alan Steadman
On the 9th November 2016, Alan Steadman from Scotland became the fifth voice.

He was a retired Civil Servant and presented a weekly local radio jazz programme for 33 years.


Additional Information

Dialling codes
The original dialling code was TIM (code 846), short for Time, which was used in London and other major cities. At smaller locations the code was 8081 or 9-8081. After the change to all-figure numbering at the end of the 1960s the TIM code was changed to 123 and elsewhere 8081 was changed to 123 also, some time in the 1990's. 

The accuracy of the speaking clock is beyond reproach, within five thousandths of a second in fact.  With a built-in crystal oscillator and microprocessor logic control, the complete apparatus is  made of solid-state microchips and occupies no more shelf space than a small suitcase does.  Contrast that with the array of motors, glass discs, photocells and valves of the original speaking clock back in 1936 - it took up most of the floor space of a small room!

Major organisations such as Network Rail, the BBC and London Weekend Television have permanent feeds of the clock from BT into their private internal phone systems so employees can check the time without making an outside call.  The timing of all ITV television programmes is synchronised to TIM as well, so when your local station goes over to ITN for the News at Ten, this is done "at the third stroke".  And perhaps the strangest - and certainly longest distance - is calls to the British speaking clock from the factory in Hong Kong that which makes the handsets for  the new VideoPlus VCR programming system.  The in-built clock is set to British time, courtesy of BT's Timeline service.

Update, by James Campbell (January 2001)
A direct feed existed to the BBC.  I remember in about 1983 visiting a BBC building on the Embankment just round the corner from Westminster tube station, it was Number 1 (can't remember the name of the road).  It was a half derelict building covered in pigeon sh*t, but on the second floor was the BBC Parliamentary Recording Unit.  It was linked via cables under the road to the Houses of Commons and Lords.  This was a place that looked like a museum but was fully operational.  The thing that I found amusing was the fact that they recorded all the material in mono on one track of the tape recorder and recorded TIM on the other track as a quick time reference.  Because the pips were rather good at breaking through to the other speech track, this particular TIM, provided by BT, did not have any pips and was known by the BBC as "seedless TIM".

What's left to see or hear of the old clocks
Not a lot is the simple answer.  The Australian clock of 1954 used to be on display at the Science Museum in London but after falling into disrepair was repaired and is now in good working order and on display.  One of the original TIM clocks was preserved and was donated by British Telecom to the British Horological Institute's museum at Upton Hall near Newark, but this too is not in working order.   People report having heard the Pat Simmons speaking clock (thanks to TIM 2000) on the following numbers: (0870 765) 8081, (0845 092) 8081, 0845 124 9068 and (0131) 477 7676.

The above numbers may not be accurate so try 01352 838081 and 01286 868081.

Other Countries who used a speaking clock and have now shut the service down:-
Australia - 2019
Ireland - 2018

TIM 2000
In the year 2000 a project was devised for creating a compact electronic speaking clock (with the Pat Simmons voice). Around 75 units were sold (there are no plans to make any more).

Further reading

Further resources on the WWW




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Last revised: June 04, 2022