Manchester attack: Last of the 22 fatalities named, as national minute’s silence held.

risk: Bomber was a ‘former subject of interest’ to MI5

Manchester bomber Salman Abedi was known to the security services and his risk to the public remained “subject to review” before he carried out his attack.

Abedi, whose sister said he “wanted revenge” for Western military strikes in the Middle East, was a “former subject of interest” to MI5, a Whitehall source confirmed.

The bomber phoned his mother hours before his attack and said “forgive me”, according to a Libyan anti-terror official.

Details of the intelligence agencies’ knowledge of Abedi came as police hunting the “network” behind his attack said they had made “significant” arrests and seized “very important” items in raids linked to the investigation.

After chairing a meeting of the Cobra emergency committee, Theresa May said the terror threat level will remain at critical, meaning another attack is expected imminently.

In an indication of the level of counterterrorism activity, a senior Whitehall source revealed that 18 plots had been foiled since 2013 in Britain, including five in just nine weeks since the Westminster attack in March this year.

It is understood the scale of the threat being dealt with by counter-terror agencies is “unprecedented” and intelligence officers faced “difficult professional judgments” about where to focus their investigations.

The source said: “MI5 is managing around 500 active investigations, involving some 3,000 subjects of interest (SOIs) at any one time.

“Abedi was one of a larger pool of former SOIs whose risk remained subject to review by MI5 and its partners.

“Where former SOIs show sufficient risk of re-engaging in terrorism, MI5 can consider reopening the investigation, but this process inevitably relies on difficult professional judgments based on partial information.”

Abedi targeted music fans at an Ariana Grande concert at Manchester Arena on Monday night, killing 22 people, including seven children, and injuring dozens in the worst terrorist incident to hit Britain since the July 7 attacks in London in 2005.

As a huge inquiry into the atrocity continued, eight people remained in custody in connection with the investigation.

Officers carried out searches at properties in Manchester, Wigan and Nuneaton.

Picture: Jeff J Mitchell. Armed police patrol as members of the public queue to lay flowers in St Ann’s Square.