Under the new definition, which comes into force on Thursday, extremism is "the promotion or advancement of an ideology based on violence, hatred or intolerance, that aims to:
1. negate or destroy the fundamental rights and freedoms of others; or
2. undermine, overturn or replace the UK's system of liberal parliamentary democracy and democratic rights; or
3. intentionally create a permissive environment for others to achieve the results in (1) or (2)."
It will apply to, but not criminalise, groups that promote an ideology based on "violence, hatred or intolerance".
It is not known which groups the government proposes to label as extremist, though it has promised to publish a list in the coming weeks