Chris GM3WOJ has posted a short history of UK Special Contest Call signs (SCCs) which have now been in use for 21 years
The holder of a UK Amateur Radio Full Licence, Full (Club) Licence or Full (Reciprocal) Licence may apply for a Special Contest Call sign (“SCC”). This call sign may only be used in amateur radio contests of no more than 48 hours duration.
The call sign will be in the format ‘G’ or ‘M’, followed by a chosen digit and a chosen suffix letter. Examples are G8Z or M7R.
Chris recalls that representations to the Regulator to issue the call signs began about 1990 but calls weren't issued until 1996.
Read GM3WOJ's Post - http://www.qsl.net/gm3woj/uksccs.htm
RSGB Special Contest Call Sign page - http://rsgb.org/main/operating/licensing-novs-visitors/online-nov-application/application-for-a-special-contest-call-sign/