3,000 Islamist extremists in Britain 'ready to attack the UK in weeks'
Terrifying numbers of British men and women - many of whom are still teenagers - are being radicalised and could stage attacks on home soil within weeks.
More than half of suspected Islamist extremists on watch lists live in London - particularly in the east and west.
But there are other hotspots in the southeast, Manchester and the West Midlands.
Investigators have also detected a significant correlation between suspects and mental health problems, which could leave them vulnerable to extremist grooming.
The anti-extremism programme Prevent now has full-time NHS staff assigned to try to identify warning signs extremist behaviour.
The revelation comes as MI5 boss Andrew Parker revealed that Britain is currently battling the "highest number" of terror plots for more than 30 years.
Mr Parker became the first MI5 director in the agency's history to give a live broadcast interview in a bid to warn the nation that the UK is under constant threat of terror attacks.
He confirmed the UK's security agencies are having to work harder than ever to protect Britons, following last last week's revelation by David Cameron that secret services had foiled six terror plots over the past year.
Mr Parker also revealed intelligence had disrupted a further nine attack plots overseas.
He warned: "That is the highest number I can recall in my 32-year career, certainly the highest number since 9/11.
"It represents a threat which is continuing to grow, largely because of the situation in Syria and how that affects our security."
Parka warned that the terror threat in the UK is changing
The new statistics suggest that the number of suspects being monitored has rocketed over 50 per cent since 2007 - when there were 2,000 suspects being watched for being seen as al-Qaeda supporters.
But the figure has soared because of the rise of Islamic State.
The security chief also warned that the "shape" of the terror threat to Britain is drastically changing, as he backed new powers for intelligence services to monitor internet communications.
Mr Parker claimed social networks such as Facebook and Twitter had a "responsibility" to share information with counter-terror officers.
He warned that Islamist extremists are reaching impressionable recruits with propaganda broadcast via social media.
He said: ""They are using secure apps and internet communication to try to broadcast their message and incite and direct terrorism amongst people who live here who are prepared to listen to their message."
Last month it emerged that security services foiled an ISIS plot to blow up the Queen at the recent VJ Day anniversary commemorations.
Ex-punk rocker Sally Jones, a key ISIS recruiter, also boasted of having another potential bomber in Scotland and two others who had so far failed to carry out attacks in the UK.