There are numerous association within the United Kingdom aiming in various ways to assist local translators, interpreters and/or translation/interpreting companies/agencies, as shown below.
Charity founded 1910; around 6000 members (400 on NRPSI).
Former part of the CIoL; breakaway group left to form the ITI.
An independent regulator for interpreters working with public services, formerly administered by the CIoL. See SPSI (below) and http://www.nrpsi.co.uk/
Trade union founded in 1958, as part of the Society of Authors. For literary translators.
Founded 1974; around 250 NRPSI members. See http://www.apciinterpreters.org.uk/
Founded in 1976; around 180 member companies. See http://www.atc.org.uk/
Founded in 1976; around 140 members, of which 75% are translators.
Founded in 2009 based on registers used since 1982.
Non-profit organization founded 1986; around 3000 members (75 on NRPSI).
Currently administered from the same premises as ITI. See http://www.asli.org.uk/
Founded in 2001. Part of Unite, the largest trade union in the UK; around 100 members. See http://www.unitetheunion.org/nupit
Formed in 2009 to represent Metropolitan Police interpreters. Its purpose is to make representations on behalf of its members, to advocate for their rights and interests, and to liaise and negotiate with work providers and official bodies. See archived web page
Founded in 2010 primarily due to concern about the effect of arrangements between Applied Language Solutions and certain police forces regarding the hiring of interpreters. Around 320 NRPSI members. See http://www.profintal.org.uk/ and http://rpsi.name/
Formed in April 2011 as successor to some of the functions of the NRPSI. [1]
See http://www.touristguides.org.uk/
Now part of a unified Tribunals framework. See http://www.tribunals.gov.uk/ImmigrationAsylum/FAQs/FAQ9.htm
Founded 1953. Not UK-centric, but lists over 120 interpreters based in the UK. See http://www.aiic.net/