Vigils for the victims of the London Bridge attack have been held in London and Cambridge.
Jack Merritt, 25, and Saskia Jones, 23, were commemorated at the services, which included a minute’s silence.
They were stabbed to death by convicted terrorist Usman Khan, 28, at a prisoner rehabilitation conference on Friday.
The BBC has learned Khan was given one of the lowest priorities for further investigation by MI5 when he left prison a year ago.
Mr Merritt and Ms Jones were both University of Cambridge graduates, and had been at an event for the university’s Learning Together programme – which focuses on education within the criminal justice system – when they were attacked.
Prime Minister Boris Johnson and Labour leader Jeremy Corbyn were among those at the vigil in the capital.
They joined London Mayor Sadiq Khan who said the best way to defeat the hatred shown in the attack was to focus on the values of hope, unity and love.
“The best way to defeat this hatred is not by turning on one another, but it’s by focussing on the values that bind us, to take hope from the heroism of ordinary Londoners and our emergency services who ran towards danger, risking their lives to help people they didn’t even know,” he said.
The London service happened less than a mile from Fishmongers’ Hall, where Usman Khan launched his attack on Friday.
Bishop of London Sarah Mullally said the vigils remembered “academics celebrating rehabilitation and finding only danger”.
She paid tribute to the workers at Fishmongers’ Hall, who she said went to work to offer hospitality, but found themselves needing to give protection.
A book of condolences is open at Guildhall Art Gallery and members of the public are invited to lay flowers outside nearby Mansion House.
Mr Merritt’s family and girlfriend attended the Cambridge service.
The victims’ families have paid tribute to their loved ones.
Ms Jones’ family said their daughter, from Stratford-upon-Avon in Warwickshire, had a “great passion” for supporting victims of criminal justice.
In a statement, Mr Merritt’s family described him as a “talented boy” who “died doing what he loved”.
Cambridge University’s vice-chancellor Prof Stephen J Toope said he was “devastated to learn that among the victims were staff and alumni”.
Toby Williamson, chief executive of Fishmongers’ Hall, praised the bravery of his staff who intervened to stop the attacker, hailing their actions as “extraordinary things done by ordinary people”.
Mr Williamson told how Polish chef Lukasz suffered five wounds to his left-hand side as he fended off the knifeman with a narwhal tusk during “about a minute of one-on-one straight combat” – allowing others time to escape danger.
Two others grabbed makeshift weapons such as fire extinguisher before the attacker fled down a staircase and then got trapped in reception.
Dr Vin Diwakar, medical director for the NHS in London, said two people injured in the attack remained in a stable condition in hospital, while one had been able to return home.
Khan, who was released from prison in December 2018 after serving half of his sentence, was later shot dead by police on London Bridge.
The BBC understands Khan was placed in the second-to-bottom category of investigations by the security service as he left jail, consistent with the grading given to most other convicted terrorist offenders as they go back into the community under a release licence.
This low level of prioritisation is assigned to offenders such as Khan because their release comes with a strict set of licence conditions.
These conditions theoretically provide suitable monitoring and oversight, such as alerts if they contact other suspects or travel outside an approved area.
Khan, the BBC has learned, was on the highest-level of such community monitoring. The overall package, in theory, relives pressure on MI5 so the security service can focus on more immediate threats.
The initial risk Khan posed to the public was thought to be minimal.
The prime minister said on Sunday that 74 people jailed for terror offences and released early will have their licence conditions reviewed.
Later that day, Staffordshire Police said a 34-year-old man had been arrested on suspicion of preparation of terrorist acts – but added there was no information to suggest the man was involved in the London Bridge attack.
The man has been named as Nazam Hussain, who was jailed in 2012 alongside Usman Khan and received the same sentence – 16 years with half of that served in prison – after pleading guilty to preparing acts of terrorism.
Following his arrest, Hussain was recalled to prison due to a suspected breach of his licence conditions. Inquiries by detectives into the potential terrorism offences are continuing, police said.
Another man, Yayha Rashid, 23, of north London, has been charged following his arrest on Sunday on suspicion of breaching notification requirements.
The Metropolitan Police said Rashid’s arrest was not connected with the London Bridge attack.
Friday’s incident comes after the UK’s terrorism threat level was downgraded on 4 November from “severe” to “substantial”, meaning that attacks were thought to be “likely” rather than “highly likely”.
The terror threat level is reviewed every six months by the Joint Terrorism Analysis Centre, which makes recommendations independent of government.
Eight people died and 48 were injured by three men who drove into pedestrians, then stabbed people in Borough Market, in London Bridge in 2017.