From the UK gov Prevent duty guidance for England and Wales here:
www.gov.uk/government/publications/prevent-duty-guidance/revised-prevent-duty-guidance-for-england-and-wales
"The white supremacist ideology of extreme right-wing groups has also provided both the inspiration and justification for people who have committed extreme right-wing terrorist acts."
"The current UK definition of ‘terrorism’ is given in the Terrorism Act 2000 (TACT 2000). In summary this defines terrorism as an action that endangers or causes serious violence to a person/people; causes serious damage to property; or seriously interferes or disrupts an electronic system. The use or threat must be designed to influence the government or to intimidate the public and is made for the purpose of advancing a political, religious or ideological cause.
‘Terrorist-related offences’ are those (such as murder) which are not offences in terrorist legislation, but which are judged to be committed in relation to terrorism."