Britain’s spies believe there may be as many as 23,000 terror suspects at large across the country.
The scale of the challenge has emerged in the aftermath of the Manchester suicide bombing that claimed 22 lives and injured 119 others.
Reports that Libyan-origin Salman Abedi had been on the radar of intelligence services had added pressure on MI5 to reveal what they knew.
Now government sources have told sections of the UK media that they believe 23,000 people with extremist tendencies are living in the UK.
About 3,000 people from the total group are judged to pose a threat and are under investigation or active monitoring in 500 operations being run by police and intelligence services.
The 20,000 others have featured in previous inquiries and are categorised as posing a “residual risk”.