SECURITY services are involved in around 500 terror probes and monitoring up to 3,000 potentially violent extremists in the UK, they have revealed.
Spooks have warned about the massive task of preventing atrocities on British soil in the wake of the devastating Manchester attack.
Authorities, facing questions about whether warning signs were missed, revealed MI5 is currently managing around 500 active investigations.
The agency has also thwarted 13 terror plots since 2013 including five since March’s Westminster atrocity.
Since Monday’s attack, counter-intelligence teams have swooped on addresses across the UK.
Eight suspects have been taken into custody and “important items” seized.
Last night the bomb squad deployed a robot as police searched a fruit seller’s home in Wigan.
There were fears they had found explosives. It is understood the flat owner is a Libyan who had been tackled to the floor the day before carrying a bag.
Neighbours were evacuated. One said: “You would often hear noises in the flat of them moving stuff around.
“He would go out in the middle of the night with this suitcase of his.
“They were always changing the carpets. He was a strange man.”
Late on Wednesday armed police tasered and detained a suspect on a grassed area near flats in Nuneaton, Warwicks.
Resident Lee Paget said: “He just lay there, they had guns with green lasers pointed on him.”
Other witnesses described police putting on boilersuits and putting bags on the man’s hands and feet.
And in Withington a house split into flats was raided with one man arrested.
Chief Constable Ian Hopkins said: “We currently have eight people who have been arrested in connection with Monday’s attack. They are all men.
“A woman who was arrested yesterday has since been released.
“The arrests have taken place in Manchester, Wigan and Nuneaton.”
As counter-intelligence officers work to uncover the terror network surrounding Abedi, questions remain if Abedi could have been stopped.
Home Secretary Amber Rudd has said he was known to the security services “up to a point”.
It emerged yesterday that Abedi was one of a larger pool of former “subjects of interest”, whose risk remained “subject to review”.
It is understood the scale of the threat being dealt with by counter-terror agencies is on an “unprecedented” scale and intelligence officers faced “difficult professional judgements” about where to focus their investigations.
A security source said: “MI5 is managing around 500 active investigations, involving some 3,000 subjects of interest at any one time.
“Where former subjects of interest show sufficient risk of re-engaging in terrorism, MI5 can consider reopening the investigation, but this inevitably relies on difficult professional judgments based on partial information.”
One former senior intelligence figure said it is an impossible task to rank each subject’s potential threat.
He added: “Knowing of someone’s radical sympathies and knowing they present a real and present danger are very different.
“So the security dilemma is how to assess who and when to investigate deeply given the resources needed for 24/7 surveillance.
“For every suspect that appears to be high priority another has to be pushed down the list.
“So who not to investigate urgently is as important a decision as who might be worth investigating.”
The official threat level, raised to the highest category of critical earlier this week, had stood at severe for nearly three years.
Shashank Joshi, of security think tank the Royal United Services Institute, said: “It’s easy, with the benefit of hindsight, to argue that these warnings were opportunities to stop the bomber.
“However, it’s also possible that these warnings were followed up, surveillance was conducted, and nothing was discovered. Authorities cannot keep monitoring a suspect indefinitely.
“There may be questions over his travel to Libya, Germany, and perhaps Syria, and his ease of return to the UK afterwards.
“It may point to weaknesses in monitoring onward travel.”
MI5 announced the figures after being slammed for not looking into calls made by the Muslim community about Abedi’s extremist views.
It was claimed that security forces missed five separate opportunities to stop the bomber.
They included a relative telling MI5 this year he was “dangerous” and a neighbour reporting suspicious activity at his home five years ago.
It takes 25 to 30 officers to monitor one suspect 24/7, meaning the UK would need 90,000 dedicated officers to cover all known extremists suspects.
The scale of the threat was again emphasised last night as the Queen Elizabeth Hospital in Birmingham was locked down in a terror scare over reports of a suspicious package.
Confused visitors were turned away as dozens of armed cops stood guard outside.
One worker said a package had been found in the prayer room and cops were searching the rest of the building.
A hospital spokesman later confirmed staff and patients were being let in and out to some wards.
A second man aged 64 has been arrested at a North London address after counter-terrorism officers stopped a 37-year-old man on Tuesday at Stansted Airport on suspicion he planned to travel to Syria.
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