An urgent crackdown on terror offenders in the UK has seen one man arrested as security services review the licensing conditions of convicted criminals in the wake of the London Bridge attack. The UK government has announced it is conducting an emergency audit of 74 offenders who have been released early from their prison sentences. It comes after convicted terrorist Usman Khan killed two Cambridge University graduates on Friday after being released from a 16-year prison sentence halfway through. He was on electronic tag when he carried out the knife rampage at London Bridge killing Saskia Jones, 23, and Jack Merritt, 25, and injuring three others. The incident happened at a prisoner rehabilitation event where the pair were working. Khan, who was wearing a fake suicide vest, was shot dead at the scene by police officers after members of the public bravely disarmed and apprehended him. On Monday a vigil was held at Guildhall Yard in the medieval heart of London to remember the victims and honour members of the emergency services and bystanders who fought the attacker. Toby Williamson, chief executive of Fishmongers’ Hall where the attack happened, said one employee, whom he identified as Lukasz, pulled a 5-foot narwhal tusk from the wall and charged at Khan, allowing others to escape. London Mayor Sadiq Khan told Monday’s vigil that, in the face of tragedy, people should “take hope from the heroism of ordinary Londoners and emergency services who ran towards danger, risking their lives to help people they didn’t even know.” The attack has pushed security to the top of the agenda in campaigning for the UK’s December 12 election. On Sunday Counter terrorism officers from London’s Metropolitan Police Service arrested and charged Yayha Rashid, 23, of north London, on suspicion of breaching notification requirements under the Counter Terrorism Act 2008. Although officials say Mr Rashid's arrest is not linked to the London Bridge attack, it comes as the government announced an urgent review of all convicted terrorists. Under the UK’s controversial automatic release system prisoners are freed halfway through their sentences. The London Bridge attack has highlighted failings in the system and raised serious questions over the authority’s ability to adequately monitor dangerous individuals. On Monday, UK Justice Secretary Robert Buckland warned that some prisoners are “not capable of rehabilitation” and extremists can “hoodwink” even the most experienced professionals. “We’ve got to get it right. There are questions to be asked about why automatic early release was being deployed,” he said. “The Prime Minister was right to say that he wants us to look again at the sentencing of terror offences.” Prime minister Boris Johnson was due to launch the Conservative Party’s security week on Monday as part of their election campaign but the initiative has been postponed following the terror incident. The father of one of the victims has urged politicians not to use his son’s death as part of their election campaigning. David Merritt said: “Don’t use my son’s death, and his and his colleague’s photos – to promote your vile propaganda. Jack stood against everything you stand for – hatred, division, ignorance.” He said he did not want his son’s death to “be used as the pretext for more draconian sentences or for detaining people unnecessarily”. Mr Johnson has criticised a previous Labour government for bringing in laws that allowed the automatic early release of the killer. Khan, Al Qaeda sympathiser, had been jailed for plotting to bomb the London Stock Exchange and other targets in 2012. Changes to the law meant that he was released in December 2018 after eight years, taking into account days he had spent behind bars before he was convicted. Khan was fitted with an electronic tag to monitor his movements and an “extensive” list of licence conditions, police said. Mr Johnson told the BBC: “I think it is repulsive that individuals as dangerous as this man should be allowed out after serving only eight years, and that's why we are going to change the law. “The key issue is that he was allowed out early. Legally there was no way of stopping him from coming out early.” Opposition Labour leader Jeremy Corbyn said he believed convicted terrorists should “not necessarily” serve their full terms, depending on the nature of their sentence and how they had behaved in prison.