A doctor has told an inquest of the “unprecedented” decision to enter the scene of the Fishmongers’ Hall terror attack to help casualties despite bomb fears.

Convicted terrorist Usman Khan fatally stabbed Cambridge University graduates Jack Merritt, 25, and Saskia Jones, 23, at a Learning Together offenders’ education conference on the afternoon of November 29 2019.

Khan, 28, who had travelled to London from his home in Stafford, had set upon Mr Merritt in the men’s toilets after strapping two large knives into his hands.

Mr Merritt suffered 12 knife wounds, including a fatal injury to his chest.

Ms Jones was stabbed in the neck in the cloakroom area and staggered on to the stairs, where she collapsed.

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Jack Merritt was one of the victims of the knife attack at Fishmongers’ Hall in London (Hickman and Rose/PA)

Two more women and a porter were also injured but survived.

Khan, who was wearing a fake suicide belt, was pursued on to London Bridge by delegates armed with a narwhal tusk and fire extinguisher, and was then shot dead by police.

Dr Andrew Milne was part of a Helicopter Emergency Medical Service (Hems) team that went to the scene in a fast-response car after being alerted to a woman stabbed in the neck.

On arrival, Dr Milne learned of gunshots and that the suspect potentially had an improvised explosive device (IED).

He told the hearing at the Guildhall that the Fishmongers’ Hall attack was the first time a Hems team had gone into a “warm zone”, confirming it was “unprecedented”.

He told jurors: “There is no specific guidance. No Hems team, as far as I’m aware, had entered a warm zone before this day.”

The court heard that, under Operation Plato, “hot zones” represent the greatest danger and “warm zones” are also dangerous areas adjacent to hot zones.

The witness said: “There was one officer that was instructing us on the number of casualties – five critical, including two in cardiac arrest.

“We were told where it was. He said it was a warm zone but very specifically said it was safe.

“So … we decided to follow the police into Fishmongers’ Hall.”

Jonathan Hough QC, counsel to the coroner, asked: “Was there any discussion about casualties being brought out to you?”

The specialist medic replied that he did not specifically recall that.

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Jack Merritt shortly before the attack inside Fishmongers’ Hall (Metropolitan Police/PA)

On entering the hall, the Hems team did a “walkaround” to assess the casualties.

Dr Milne said: “Given the hazards at that scene, specifically the potential IED on the perpetrator, we felt we needed to get the patients we had a chance of helping out to the casualty clearing point as fast as possible.

“Saskia did not have a chance of recovery, had been in cardiac arrest for too long and, (given) the blood loss and the region where she was stabbed, we did not have a hope of reversing cardiac arrest.”

But he felt there was a “chance” to save Mr Merritt and wanted him to be taken out first.

The Hems team spent four minutes inside the hall before heading to the casualty clearing point.

At around 2.28pm, Dr Milne and his colleague performed a thoracotomy on Mr Merritt, who had been dragged out on a Sked stretcher.

The doctor described the moment he realised Mr Merritt could not be saved.

He told jurors: “I can feel the heart is very empty. At that point I knew the patient had bled to death. Jack had bled to death.”

Mr Merritt was pronounced dead at 2.33pm.

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Usman Khan (left) and Saskia Jones (right) sit at a table together at the prisoner rehabilitation event at Fishmongers’ Hall, near London Bridge (Metropolitan Police/PA)

London Ambulance Service paramedic Carlton Cullinan, who is trained to work in a “warm zone”, went into the hall ahead of Hems, the court heard.

Describing the scene, he said: “It was very crowded, a lot of blood. There was blood down the staircase at the front.”

He added that it was “just generally messy and chaotic”.

He went into a security office where Mr Merritt was being given CPR by police officers with a defibrillator.

Mr Cullinan said: “Our plan was to extricate Jack to our casualty collection point near our cars.

“We have, as part of the tactical response unit, these devices called a Sked.

“I was instructing them how to get him on to that. It is designed to be dragged. You cannot do chest compressions and extricate.”

Mr Hough asked: “What’s the rationale behind taking somebody out of the scene even when that involves ceasing CPR when there is lots of police to protect the scene?”

The witness replied: “To get out of the warm zone, to keep them safe.

“The idea is to get these patients out for more extensive treatment from more advanced clinicians and doctors who can perform surgeries and potentially help save the patient.”

Asked why it was so important, he said: “The Hems team are also able to give blood to help with the circulation, provide oxygen to tissue.”

Mr Cullinan said he saw Hems medics in the foyer of the hall as Mr Merritt was being dragged out on the Sked stretcher.

A firearms officer felt a “wave of dread” on being told the Fishmongers’ Hall attacker had an IED, jurors heard.

The officer, referred to as YX97, immediately realised that if the suspect detonated the device, anyone in the immediate vicinity would “almost certainly” be killed or seriously injured, jurors were told.

The officer shouted at members of the public to “run and take cover”, according to a statement read in court.

On learning that there were multiple casualties inside the hall in need of a defibrillator and first aid, the officer “literally threw” the kit at a uniformed colleague.

The officer went on to tell paramedics it was a “warm zone” and they could come in to extract the casualties.

The officer said: “I saw a young male being put on to a stretcher. I said, ‘you need to scoop and run’. The male appeared to be deceased. I saw another two injured, one walking wounded.

“It was a scene of devastation with blood everywhere.”

The inquest before Coroner Mark Lucraft QC was adjourned until Monday.