The convicted murderer who helped foil the terror attack on London Bridge last November armed only with a Narwhal tusk will see his sentence cut following an intervention by the Queen.

Steven Gallant, 42, was on day release at the event for reformed prisoners in Fishmonger’s Hall when he helped end Usman Khan’s rampage, which left two Cambridge graduates dead.

Jack Merrit, 25, and 23-year-old Saskia Jones – both part of the Learning Together scheme to help prisoners access education – were killed, while several others were wounded.

It was Gallant’s first time out on licence after being jailed for life with a minimum term of 17 years in 2005 for the murder of a firefighter in Hull.

He helped restrain Khan, who was wearing fake suicide vest and armed with two knives, before the terrorist was shot dead by police.

The Ministry of Justice revealed on Saturday that the Queen had employed the little used “Royal Prerogative of Mercy” to bring Gallant’s case before the parole board 10 months early.

Jack Merritt funeral
Mourners gather for Jack Merritt’s funeral (Aaron Chown/PA)

The monarch used the power on the advice of Lord Chancellor Robert Buckland. A spokesman for the Ministry of Justice (MoJ) said: “The Lord Chancellor has granted Steven Gallant a Royal Prerogative of Mercy reducing his minimum tariff of 10 months in recognition of his exceptionally brave actions at Fishmongers’ Hall, which helped save people’s lives despite the tremendous risk to his own.”

The final decision ultimately rests with the parole board, but it is highly unlikely Gallant will be denied his freedom.

It is understood he has been a model prisoner who has expressed remorse for his crimes and has not faced any punishment or loss of privileges for the past 10 years.

Jack Merritt’s father David, 55, welcomed the news.

He told the Daily Mirror: “Steve fully deserves this pardon, or reduction in sentence.

“It is fantastic. He was very close to Jack and he turned his life around and reformed. I am really pleased for him.”

Gallant has also participated in a number of interventions, including addressing previous substance abuse, and is in the process of studying for a business degree.

Ex-prisoner John Crilly, who was hailed a hero after he tackled Khan with a fire extinguisher during the attack, told Sky News he was “ecstatic” for Gallant.

But he added: “I think if you’re going to do anything, do something more substantive, maybe give him a proper pardon.

“Because like I say, I think it’s just a reduction in his sentence, which, apart from getting out 10 months early, has no real significance to it.”

Gallant was one of two men convicted of the murder of Barrie Jackson, 33, who was beaten to death outside a pub in Hull.

The pair lay in wait for Mr Jackson outside the Dolphin after believing he attacked Gallant’s girlfriend.

Jackson was sprayed with CS gas and beaten so savagely with a hammer by a group of men that paramedics were unable to find his mouth.

The previous year, Jackson had himself been cleared of the attempted murder of a 64-year-old woman – stamping on her face and dumping her unconscious in a skip. He was convicted of assault.

Jackson’s student son Jack, 21, told the Mirror: “In my mind, Gallant has nearly done his time and if someone has undergone rehabilitation and change, which it seems he has, then it’s fair enough.”