Dominic Grieve MP has said it is "noteworthy" that a number of perpetrators behind terror attacks in the UK last year were already known to MI5.
The chairman of the government's Intelligence and Security Committee appeared on the breakfast show to discuss the Committee's new report, which outlines how the security services can be improved, particularly with regards to preventing terror attacks.
Mr Grieve said "quite a few" of the attackers were considered "closed subjects of interest" by MI5, including Manchester Arena bomber Salman Abedi, who had been known to the security agency since 2014.
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There are around 3,000 subjects of interest currently being monitored by MI5, and 21,000 closed subjects of interest.
"A closed subject of interest is someone that has been of interest to the security services but as things stand at the moment is not thought to pose a great risk," Mr Grieve told Julia Hartley-Brewer.
"There are 21,000 of those and it's noteworthy that those who perpetrated the attacks last year, quite a few of them were people who were within that category."
Mr Grieve said he hoped the new report would help the security services to review how closed subjects of interest were "dealt with", and how to spot that they had become "much more dangerous and posing a risk".
"The question we were looking at is what were the flag markers of their behaviour which should have registered differently with MI5 and would have alerted them to the face they were now much more dangerous.
"That's what this report is about, how do you join up the dots better?".