Police officers stand behind the cordon at the scene of a stabbing near London Bridge, in which two people were killed, in London, England, November 30, 2019.
Khan is dead, one is still in prison and another was convicted for a further terror plot - leaving six back on the streets, it is believed.
The Mayor of London, Sadiq Khan, said: "Like many, I will never forget the bravery of ordinary Londoners and the emergency services who risked their own lives to save others. And it's also by drawing inspiration from the lives of Jack and Saskia, who from an early age chose to dedicate themselves to helping others".
A minute's silence was observed at Guildhall Yard in central London and Cambridge.
The UK paid tribute to victims of Friday's terror attack in London as politicians, friends and family gathered with members of the public in the British capital and Cambridge on Monday.
Williamson told Sky News that Lukasz, wielding the tusk, fought one-on-one with Khan for about a minute and suffered cuts on his arm, but didn't "flinch for a moment".
The attack has pushed security to the top of the agenda in the election campaign.
Convicted of terror offences in February 2012, he was released from prison on licence in December 2018, halfway through his 16-year prison sentence.
Billions of pounds have been stripped from British public finances over the last 10 years, during which the ruling Conservative Party has sought to reduce public debt by shrinking state-run services.
However, the Monday papers in the United Kingdom - including the Daily Mail and The Express - reported on a "terror blitz", following orders from Prime Minister Boris Johnson to "crack down on extremists" in the wake of the attack. Jack Merritt, 25, and Saskia Jones, 23, who both died in the attack, worked as coordinator and volunteer respectively.The Ministry of Justice declined to comment.
The family of Mr Merritt also cautioned against knee-jerk responses.
"We know Jack would not want this bad, isolated incident to be used as a pretext by the government for introducing even more draconian sentences on prisoners, or for detaining people in prison for longer than necessary", they said in a statement.
"Don't use my son's death, and his and his colleague's photos to promote your vile propaganda", Merritt said on Twitter.
"Jack stood against everything you stand for - hatred, division, ignorance", he said.
Corbyn said Conservative cuts to community policing, probation, mental health, youth and social services could "lead to missed chances to intervene in the lives of people who go on to commit inexcusable acts". Police said on Monday he had been returned to prison for breaching his release conditions.
"I am devastated to learn that today's hateful attack on London Bridge may have been targeted at staff, students and alumni attending an event organised by the University of Cambridge's Institute of Criminology". The group did not provide any evidence.