Most UK telephone equipment can be identified by the manufacturers codes stamped on them.  All British Post Office equipment is marked in some way and these markings greatly assist in identification and dating.  Even small components are generally marked and these markings will ascertain whether the whole item is in fact genuine.

Always look inside the phone - they should have a diagram inside which may indicate the manufacturer or model number.

British Post Office (BPO)
In most cases the markings consist of a number, followed by a manufactures code, followed by a year.

In the picture to the right it is in a slightly different format with No. 162F being the telephone number and the S-32 meaning it was made by Siemens in 1932.

Another example would be the marking 1/232L S55 and this would be a Telephone No. 1/232L, made by Siemens in 1955.

The numbers 234 and 235 are occasionally shown.  These are Mark numbers and is how the GPO designated updates; 234 being the Mark 1, 235 being the Mark 2 etc.

On wooden apparatus and Candlestick telephones you may find a number crossed out and another number stamped on.  Latter equipment may have a plastic sticker, with the description on, covering the old description.  This is where the apparatus went back to the factory for repair or was made into a different item.  i.e. No. 150 crossed out and No. 156 stamped next to it.

On Candlestick telephones the number is on the transmitter support, on wall telephones stamped on the back, on 100 & 200 Bakelite telephones on the base and with 300 types the model number is on the base plate and also printed on the internal chassis - between the bell gongs.

Inside the phone you should find a circuit diagram that should confirm the number on the telephone base.  GPO telephone N diagrams are always the telephone number plus 100 i.e. Telephone No. 232 is diagram N332.

There will almost certainly be a blue stamp near these markings and this would be the GPO quality assurance stamp.  Sometimes these are stamped on a white painted area (the paint covers old stampings).

The Automatica Electrica Portuguesa company that produced 300 type telephones on licence from ATM. Sold in Portugal only.

The telephone base will have the model number which will be prefixed by either an L or a T.  Inside there should be a diagram and the diagram will only show the diagram number which will be prefixed by an L.  These diagram numbers DO NOT represent the model or part number and are the diagram number only.

British Ericsson (ETL)
This company normally prefixed it's model numbers and diagram numbers with an N except the very early models.  So on the base expect to see a marking something like N1016 - this would be the model number.  The part number may be extended i.e. N1016A16, but it's base number is N1016 and the variant of this would be A16.

Inside the case there should be a diagram and these are numbered and start with the letter N as well.  These diagram numbers DO NOT represent the model or part number and are the diagram number only.  In the Ericsson telephone list you will find that many diagram numbers of the "n" series can be cross referenced as an aid to identification.

Check the case for an ETL marking on the rear.

GEC used the letter K followed by three or four digits, they also used a combination of two letters followed by 4 numbers and finally the prefix letters TEL for their telephone part numbers i.e. K7995, IT2201 or TEL23D.  Other products started with a lettered prefix as well.  GEC generally did not mark the model number on the base.

GEC diagrams are prefixed with KS.  Diagram numbers DO NOT represent the model part number.

This is an Indian company that manufactured telephones similar looking to GPO telephones.  Whilst these are reasonable telephones in their own right, they are sometimes passed off as original GPO telephones.  They normally have oblong vents on the base with very small holes and a non-GPO dial.  Made for the Indian Market.  Normally marked with a DJL number, on a pasted paper label, on the base.  Click here for ITI telephones

Siemens Bothers
There telephone generally have Siemens Brothers stamped on the base but there is no identification of the model number.

Inside there should be a diagram and the diagram with show both the model number and the diagram number.  The diagram number will be prefixed with the letter T.  Early Siemens Brothers equipment will have a model number prefixed with the letter Q.

TMC diagrams are prefixed with S and so are some of the phones.  The boat phones are normally prefixed with the letter "L" followed by two digits.  Some phones are prefixed with the letter "T" followed by three digits.


Want to find a telephone but are completely confused - then follow this link.

Some telephone items are reproductions and very good ones at that!  It has been noted that some reproductions even have numbers crossed out on the cases to make them look more authentic.  Many are now repainted as well - dealers call it "refinishing"!

Collectors information on all old GPO telephones Click here  

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Last revised: July 24, 2023