These prefixes are used for UK and Crown Dependency amateur callsigns, unless otherwise stated suffixes may be one, two or three characters in length:

• Foundation M3, M6, M7
• Intermediate 2#0, 2#1, M8, M9
• Full G0, G1, G2, G3, G4, G5, G6, G7, G8, M0, M1, M5
• Special Event Station GB0, GB1, MB0, MB1
• Analog Voice Repeaters GB3 + two letter suffix
• Digital Voice Repeaters GB7 + two letter suffix
• Beacons GB3 + three letter suffix
• Gateways/Data Stations MB7 + two or tree letter suffix

If a callsign starts with 2 a Regional Secondary Locator must be inserted immediately after the 2 e.g. 2E0ABC for a station in England. For G and M callsigns the use of a RSL is entirely optional

The prefixes of UK callsigns have changed considerably over the past century, the regional prefixes we have today only exist because at various times the RSGB made representations to the regulator to create them. Prior to the 1990's the term “Regional Secondary Locator” (RSL) wasn't used, either “Callsign Prefix” or “Callsign Zone” were used instead.

Up until July 1991 UK amateur callsigns used only the G prefix. The introduction of the Novice (Intermediate) licence saw the use of the 2 prefix, it is likely this also resulted in the use of the term “Regional Secondary Locator” instead of Prefix.

In September 1989 RadCom the RSGB suggested the DTI use of the “M” prefix for Novice callsigns but “2” was eventually chosen by the new regulator, the Radiocommunications Agency (RA) in 1991

These three QSL cards illustrate the variations the club station of the Stirling and District Amateur Radio Society had in the space of just 10 years: G-6NX, GC-6NX, back to G-6NX, then GM-6NX. Thanks to GM6DX for images

In 1927 UK obtained the ITU country prefixes of M, G, and 2 from the ITU along with V and Z which were used in the Dominions and Empire.

Prefixes were discussed in the July 1936 issue of the RSGB T & R Bulletin. At the time amateurs in the UK and Crown Dependencies had just two prefixes, either G which covered Great Britain & CDs and GI for Northern Ireland. The GC prefix used briefly in Scotland had reverted back to G and the former GW prefix, used for the Irish Free State, had been replaced by EI.

The view was expressed that both Scotland and the Channel Islands should be counted as a separate entities with a unique prefix but it was not felt the Isle of Man deserved a unique prefix and Wales was regarded as an integral part of England, so should have the same prefix. However, within a few months the RSGB would shift its position regarding a Welsh prefix

In 1937 at the request of the RSGB the regulator, the General Post Office (G.P.O), introduced prefixes GM for Scotland and GW for Wales.

In 1946 the G.P.O agreed to an RSGB request to create the prefix GC for the Channel Islands, December 1946 T & R Bulletin

In 1947 the RSGB changed its mind over a prefix for the Isle of Man and requested the G.P.O. to create one, June 1947 T & R Bulletin

In 1977 the Channel Island GC prefix was replaced by GU for Guernsey and GJ for Jersey leading to the creation of a new DXCC entity for amateurs to collect, December 1976 RadCom

In 1995 new RSL's were introduced for Club stations, this could be used to identify those stations permitted to send Greeting Messages from unlicenced persons, a facility introduced at the same time, but the use of the Club specific RSL's was optional and many clubs stuck to the RSL they'd always used.

In 2000 Short Contest Callsigns with MZ and GZ prefixes were introduced for use in the Shetland Islands, RSGB December 2000 RadCom announcement

In 2008 Ofcom said they did not regard the RSL as being part of the core UK callsign and in 2013 stated the words in the licence actually meant the Main Station RSLI should be used when visiting other regions but they were happy for amateurs to continue with existing practice of changing RSL if they wished.

In 2014 Ofcom proposed making it clear in the licence that the RSL was optional, this generated opposition from the RSGB so Ofcom decided not to add clarity to the licence at that time but Ofcom continued to consider that amateurs with M or G callsigns could either omit the RSL or give the RSL for the region they were visiting if they wished.

In 2014/15 at attempt was made by Cornish amateurs to get the “K for Kernow” RSL issued for use in Cornwall. While Ofcom appeared to be supportive of the idea and issued a temporary “K” RSL during 2016 the RSGB did not support a permanent “K” RSL so it did not happen https://web.archive.org/web/20160408145201/https://gb2gm.org/k-for-kernow/ : Poldu report on RSL

Correspondence from Ofcom and RSGB

In 2023 Ofcom again proposed changing the licence words to make it clear the RSL was optional, this time the RSGB did not oppose it.

In August 2025 RSGB Director Stewart Bryant G3YSX posted an explanation:

At the request of the RSGB the regulator agreed to the use of these special RSL's for a limited period.

From 4 June to 12 June 1977 all UK licensees were allowed to use the prefix “GE” instead of the normal country prefix, to commemorate the Silver Jubilee of Her Majesty, Queen Elizabeth II.

From 5 May to 12 May 1985 the GV prefix was used from all parts of the UK in the period . The prefix was used to celebrate the 40th anniversary of the end of WWII (“Peace in Europe” according to QSL cards). The GV prefix was used for special event calls, not personal calls (unlike the GE & GQ prefix). The “V” possibly signified Victory.

During December 2001 the three character callsign “2MT” was used by the Chelmsford Amateur Radio Society special event station set up at the old Marconi factory in New Street, Chelmsford, Essex, to commemorate Marconi's first trans-Atlantic wireless transmission. The station used all Marconi Equipment.

During the whole month of June 2002, all UK licensees were allowed to use the prefix “GQ”, “MQ” or “2Q”, as appropriate, instead of the normal country prefix, to commemorate the Golden Jubilee of Her Majesty, Queen Elizabeth II. Also during this period, the special callsign “GB50” was used by a commemorative station set up at Windsor Castle, England. This callsign was unique in that it did not contain any suffix letters.

From 1 September 2009 to 20 October 2010, special event stations commemorating the centenary of the Girl Guide movement could request callsigns in the GG100xx or GG100xxx series.

From 29 April 2011 to 09 May 2011 the prefixes “GR”, “MR” & “2R” were allowed, via pnline application for an NoV, to be used by individuals as special temporary calls to celebrate the Royal Wedding of H.R.H Prince William to Miss Catherine Middleton. Club special calls for this event were of the standard “GB” type, although, due to administrative errors, some Clubs applied and were issued the NOV but were not allowed to use it.

Source: Highfields Amateur Radio Club

Ofcom stores callsigns in their licensing database in the base format for the UK, the Regional Secondary Locator (RSL) is not regarded as part of the call sign for Regulatory purposes.

• Ofcom Callsign Spreadsheet 11 September 2025

• Ofcom Forbidden callsign suffixes 5 December 2024

• M0PYL Callsign Lookup See at a glance which calls are available for issue

ITU Radio Regulation state a callsign must comprise:

19.68 1) – one character (provided that it is the letter B, F, G, I, K, M, N, R or W) and a single digit (other than 0 or 1), followed by a group of not more than four characters, the last of which shall be a letter, or – two characters and a single digit (other than 0 or 1), followed by a group of not more than four characters, the last of which shall be a letter. (WRC-03)

19.68A 1A) On special occasions, for temporary use, administrations may authorize use of call signs with more than the four characters referred to in No. 19.68. (WRC-03)

19.69 2) However, the prohibition of the use of the digits 0 and 1 does not apply to amateur stations.

ITU Radio Regulations Article 19 Identification of a Station

RF-Man UK Callsign page Shows approximate date callsigns first issued

Short Wave Magazine April 1949 page 134 (PDF page 56) Callsigns in the 1920's