Dont need to "carry out acts of terrorism" to be deemed a terrorist organisation. The Home Secretary has the power to proscribe whoever it is deemed "desirable" to be called such. Look for the catch all inside my !!....!! notations on this government pamphlet.
What is a proscribed organisation?
. Under the Terrorism Act 2000, the Home Secretary may proscribe an organisation if she
believes it is concerned in terrorism, and it is proportionate to do. For the purposes of the
Act, this means that the organisation:
• commits or participates in acts of terrorism;
• prepares for terrorism;
!! • promotes or encourages terrorism (including the unlawful glorification of terrorism); or
• is otherwise concerned in terrorism. !!
What determines whether proscription is proportionate?
A. If the statutory test is met, the Secretary of State will consider whether to exercise her
discretion to proscribe the organisation. In considering whether to exercise this discretion,
the Secretary of State will take into account other factors, including:
• the nature and scale of an organisation’s activities;
• the specific threat that it poses to the UK;
• the specific threat that it poses to British nationals overseas;
• the extent of the organisation’s presence in the UK; and
!! • the need to support other members of the international community in the global fight !!
against terrorism
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/612076/20170503_Proscription.pdf