• British-based terrorists are as ethnically diverse as the UK Muslim population, with individuals from Pakistani, Middle Eastern and Caucasian backgrounds. MI5 says assumptions cannot be made about suspects based on skin colour, ethnic heritage or nationality.

• Most UK terrorists are male, but women also play an important role. Sometimes they are aware of their husbands’, brothers’ or sons’ activities, but do not object or try to stop them.

• While the majority are in their early to mid-20s when they become radicalised, a small but not insignificant minority first become involved in violent extremism at over the age of 30.

• Far from being lone individuals with no ties, the majority of those over 30 have steady relationships, and most have children. MI5 says this challenges the idea that terrorists are young men driven by sexual frustration and lured to “martyrdom” by the promise of beautiful virgins waiting for them in paradise. It is wrong to assume that someone with a wife and children is less likely to commit acts of terrorism.

• Those involved in British terrorism are not unintelligent or gullible, and nor are they more likely to be well-educated; their educational achievement ranges from total lack of qualifications to degree-level education. However, they are almost all employed in low-grade jobs.

The researchers conclude that the results of their work “challenge many of the stereotypes that are held about who becomes a terrorist and why”.

Crucially, the research has revealed that those who become terrorists “are a diverse collection of individuals, fitting no single demographic profile, nor do they all follow a typical pathway to violent extremism”.

The security service believes the terrorist groups operating in Britain today are different in many important respects both from Islamist extremist activity in other parts of the world and from historical terrorist movements such as the IRA or the Red Army Faction.

The “UK restricted” MI5 “operational briefing note”, circulated within the security services in June, warns that, unless they understand the varied backgrounds of those drawn to terrorism in Britain, the security services will fail to counter their activities in the short term and fail to prevent violent radicalisation continuing in the long term.

It also concludes that the research results have important lessons for the government’s programme to tackle the spread of violent extremism, underlining the need for “attractive alternatives” to terrorist involvement but also warning that traditional law enforcement tactics could backfire if handled badly or used against people who are not seen as legitimate targets.

The MI5 authors stress that the most pressing current threat is from Islamist extremist groups who justify the use of violence “in defence of Islam”, but that there are also violent extremists involved in non-Islamist movements.

They say that they are concerned with those who use violence or actively support the use of violence and not those who simply hold politically extreme views.