There are numerous associations within the United Kingdom aiming in various ways to assist local translators, interpreters and/or translation/interpreting companies/agencies, as shown below (in approximate order of age).
Private Limited Company by guarantee without share capital use of 'Limited' exemption, founded in 1986; over 3000 members.
In 2016 became ACCI (see below) - website dead since that time (archive copy) Not to be confused with the Asylum and Immigration Tribunal (see below).
Founded as company in October 2019 "to seek protection of title [and] ensure the regulation of the profession".
Website ("ait-professionals.com") never set up, but active on Facebook, LinkedIn, Instagram (largely reverted to personal content) and (Skilliga).
See http://www.apciinterpreters.org.uk/ See https://www.nrpsi.org.uk/ An independent regulator for interpreters working with public services, founded in 1994 and administered by the CIOL until 2011.
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 http://www.somiukltd.com/ Founded in 2009 (incorporated in 2010)[1] primarily due to concern about the effect of arrangements between Applied Language Solutions and certain police forces regarding the hiring of interpreters.
Successor to AQTI, renamed in 2016 as a "global not-for-profit body for professional interpreters" (but still clearly UK-centric).
Administered by Signature (previously CACDP, the Council for the Advancement of Communication with Deaf People).
See http://www.lipspeaking.co.uk See https://bsllegal.org/ Not all Blue Badge tourist guides have to have interpreting skills, but many do, taking language exams administered by the Institute of Tourist Guiding and tested to CIOL or Foreign and Commonwealth Office standards.
Not UK-centric, but lists over 130 interpreters based in the UK / Ireland (as part of a global network of 3000).