An extraordinary account of the “blood, screaming and chaos” inside London’s Fishmongers’ Hall and selfless acts of bravery has been given on the day emotional vigils took place to honour Jack Merritt and Saskia Jones whose lives were taken so brutally in last Friday’s terror attack.

After the dramatic scenes of how ordinary members of the public challenged convicted terrorist Usman Khan on London Bridge, where he was shot dead by police, Toby Williamson, Chief Executive of the Fishmongers’ Hall, recounted what happened there moments before at the prisoner rehabilitation seminar.

He explained how Lukasz, a kitchen porter in his early thirties, cleaning glasses in a basement, heard a commotion and rushed upstairs. Confronted by a knife-wielding Khan, he “makes a choice and goes towards the trouble,” declared Mr Williamson.

“There’s blood, there’s screaming, there’s chaos. Lukasz pulls off the wall this long stick. He charges towards the bad guy and impacts him on the chest…He is buying time; he allows others to escape, to move to adjacent rooms and has about a one minute one-on-one straight combat.”

Khan slashed the porter five times on his left side. “But,” explained Mr Williamson, “he has done what he needed to do.”

Two other men then joined the fray, one armed only with a fire extinguisher and another who has ripped a narwhal tusk from the wall.

“It was pretty gruesome. The terrorist decided he was outnumbered. He runs for it,” recalled Mr Williamson, who explained how the “next bit of hell” occurred at reception.

“Gareth is pushing the door shut as good as he can so Dawn, a yard behind, can get on the telephones, hit the alarms.”

Blocked, Khan moved to the cloakroom where Sandra and Anna experienced a “hell of a time” before a “great showdown” occurred in the entrance hall with Lukasz “leading the charge” helped by a “pretty cool customer” called Andy.

The terrorist made good his escape onto London Bridge pursued by Lukasz, urging passers-by to run away but, Mr Williamson recalled, members of the public ignored his advice and joined in the pursuit.

“The man with the fire extinguisher, the man with the narwhal tusk, they are all in there. Lukasz is losing strength on his left side but, I tell you what, his job is done. The police are there,” added Mr Williamson.

Others also helped restrain Khan, including an off-duty police officer, who disarmed the terrorist, another kitchen porter called Mohammed, on his lunch-break, and James Ford, a convicted murderer, who was attending the rehabilitation seminar.

Lukasz, who has been discharged from hospital, will on Tuesday celebrate his birthday at home with his partner. He is set to receive a medal for bravery from the Polish Government.

On Monday, two vigils took place for Mr Merritt, 25, and Ms Jones, 23.

In Cambridge, hundreds of people turned out to pay their respects. Mr Merritt’s girlfriend Leanne O’Brien, a 25-year-old veterinary science student, was comforted by his father David as she broke down in tears, clutching a soft pink toy.

At London's Guildhall Yard, Boris Johnson and Jeremy Corbyn stood side-by-side to pay their respects to the victims, observing a minute's silence alongside members of the public.

Sadiq Khan, the London Mayor, called for people to come together “in a spirit of defiance” against terrorism and work for a future "not defined by hatred but defined by hope, unity and love".

He added: "We come together this morning as Londoners to remember, to honour and to mourn the innocent lives lost as a result of this horrific terrorist attack on Friday.

"The best way to defeat this hatred is not by turning on one another but by focusing on the values that bind us."