Part 2 of the Terrorism Act 2000 (c. 11) makes provision about proscribed organisations (including setting out offences in relation to such organisations in sections 11 to 13). An organisation is proscribed if it is listed in Schedule 2 to that Act or, in most cases, if it operates under the same name as an organisation so listed (section 3(1)).
Link: The Proscribed Organisations (Name Change) Order 2019
Source: Legislation .gov.uk
