MI5 could not have prevented the Fishmongers’ Hall attack despite earlier intelligence that Usman Khan wanted to “die and go to paradise”, a senior security officer has told an inquest jury.

An internal investigation immediately after the atrocity, in which the homegrown jihadi killed Cambridge graduates Saskia Jones, 23, and Jack Merritt, 25, and injured three other people at a prisoner education event in London on November 29 2019, found the security service could not have stopped it.

The 28-year-old convicted terrorist, from Stafford, who launched his bloody rampage with two knives and a fake suicide belt, was shot dead by police after being chased by delegates on to London Bridge.

Inquests at City of London’s Guildhall into the deaths heard that Khan was allowed to attend the event despite intelligence that he would “return to his old ways” upon his release from prison 11 months earlier.

On Thursday, a senior MI5 officer, known as Witness A for legal reasons, said security services remained sceptical of Khan but there was no reason to feed concerns over his attendance at the central London event into meetings of Mappa (multi-agency public protection arrangements) beforehand.

She said: “At that time, there was no intelligence to suggest he should not be allowed to attend.

“On the flip side, preventing someone from doing something can have ramifications.”

The witness told the court that MI5’s review after the Fishmongers’ Hall attack concluded that it “could not have taken any actions or materially changed the outcomes of this case”.

It added: “The investigative and operational decisions taken by MI5 in this case were sound.”

Giving evidence from inside a white cube, referred to in a moment of rare levity by the coroner as a “tardis”, the witness said detecting Khan’s preparations would have required 24/7 surveillance which on the intelligence available would have been “disproportionate, likely unjustified, and probably unlawful”.

The court heard Khan was one of 3,000 active “subjects of interest” under investigation, and that nearly 30 terror plots had been foiled since 2017.

She said the security service first became aware of Khan in 2008, as a member of terror group al-Muhajiroun (ALM).

He was linked to a plot to attack the London Stock Exchange and jailed for planning a terror camp abroad.

The officer said MI5 was aware that Khan had been involved in violence in prison.

Jonathan Hough QC, counsel for the coroner, asked: “Was there also evidence he wanted to die and go to paradise?”

Witness A replied: “There was information to that effect.”

Jurors were told that Khan had retained contact with his co-defendants and other terrorists outside prison.

But, in 2015, MI5 took the decision to close its investigation into him.

We cannot investigate people forever

Asked whether, in hindsight, she feels that was the right decision, Witness A replied: “I do.

“We had carried out quite a significant period of investigation while he was in prison, we received a steady stream of intelligence while in prison, and we saw no activities of national security concern, therefore it was the right time to close the investigation.”

She added: “We cannot investigate people forever.”

Witness A said MI5 had shared with counter-terrorism police two strands of prison intelligence before his release, that Khan was preparing “to return to his old ways”, and that he was aspiring to carry out an attack upon release.

She said both strands of intelligence were uncorroborated, but the detail about any apparent intention to commit an atrocity was not passed on to Mappa.

Jurors heard that MI5 opened a new investigation into Khan in August 2018 in readiness for his release into the community in December.

Agents went on to carry out heightened surveillance on Khan and remained “sceptical” that he may be complying with the terms of his release in order to avoid scrutiny.

At a meeting on November 18 2019, MI5 found out about the trip to London but was unaware of the date, the venue or who would be there, the court heard.

Witness A told jurors that, at the time, security services were looking to close their investigation into Khan and saw the Learning Together date as an opportunity to gain reassurance from enhanced surveillance.

She confirmed that the risk of attack planning was not discussed at the joint operations team meeting nor the potential risk of Khan going to the London event.

Mr Hough said: “Looking back, even without the awful knowledge of the attack that followed, would you not accept that there ought to have been some consideration at this stage of the risk of the event, even if only to decide the risk was limited and was a risk that could be properly taken?”

Witness A conceded: “I think given the awful tragedy that occurred, it would certainly have been helpful to have that discussion at this meeting.”

She was asked what MI5 would have done if it had come to light that Khan had purchased items, including four kitchen knives.

The witness said MI5 would have immediately taken steps to take “executive action” and arrest him.

The inquests into Ms Jones and Mr Merritt’s deaths continue.