Radicalisation refers to the process by which a person comes to support terrorism and forms of extremism. There is no single way of identifying an individual who is likely to be susceptible to an extremist ideology. It can happen in many different ways and settings. Specific background factors may contribute to vulnerability which are often combined with specific influences such as family, friends or online, and with specific needs for which an extremist or terrorist group may appear to provide an answer. The internet and the use of social media in particular has become a major factor in the radicalisation of young people.

Extremism is vocal or active opposition to fundamental British values, including democracy, the rule of law, individual liberty and mutual respect and tolerance of different faiths and beliefs. This also includes calls for the death of members of the British armed forces, whether in this country or overseas.