The father of London Bridge terror victim Jack Merritt has said his son would be "livid" that his death is being used to further an "agenda of hate".
Cambridge University graduates Mr Merritt, 25, and Saskia Jones, 23, were both stabbed to death by 28-year-old convicted terrorist Usman Khan during a prisoner rehabilitation event they were supporting in London on Friday.
Boris Johnson and Jeremy Corbyn both paid tributes to the victims at a vigil in London on Monday morning amid continued criticism of the politicisation of the incident amid the election campaign.
Writing for the Guardian on Monday, David Merritt said his son would be "seething at his death, and his life, being used to perpetuate an agenda of hate that he gave his everything fighting against".
He earlier condemned Mr Johnson's reaction to the death of his son, writing his son "would not wish his death to be used as the pretext for more draconian sentences or for detaining people unnecessarily."
Mr Johnson has vowed to take steps to ensure people are not released early when they commit serious offences.
In response to Mr Merritt's statement, the Prime Minister said he felt a "huge amount of sympathy" for the family of Ms Jones and Mr Merritt but added too many people were being released automatically, something he believed needed addressing with legislation.
Mr Johnson and Mr Corbyn stood side-by-side and were joined by Mayor of London Sadiq Khan and members of the public in observing a minute's silence for the former University of Cambridge students.
The girlfriend of Mr Merritt broke down in tears as she attended a vigil in his memory in Cambridge.
Leanne O'Brien wept and clutched a cuddly toy as she was comforted by family and friends at the remembrance ceremony.
A friend of Ms Jones, James Morgans said she "wouldn't want people to be sad".
He also paid tribute to Ms Jones, saying: "She was just a happy person, if you went in a room with her, even if you were in tears, you would leave happy.
"She had so much love to give and even to the end she was working as a volunteer."
He continued: "She was just kind, she was just so kind."
Another friend, Lauren told ITV news that Saskia has "always been a hero".
She said that Saskia "has always been a hero, she was always helping other people."
She added: "I'm just going to miss her so much."
The Mayor called for London's residents to come together following the killings and work together for a future "not defined by hatred but defined by hope, unity and love".
Mr Khan said: "The best way to defeat this hatred is not by turning on one another but by focusing on the values that bind us."
He also thanked the public and the emergency services who "ran towards danger, risking their lives to help others".
It comes as West Midlands Police said a 34-year-old man arrested in Stoke-on-Trent on suspicion of preparation of terrorist acts has been recalled to prison due to a suspected breach of his licence conditions.
He has been named in reports as Nazam Hussain who was jailed with Usman in 2012 for terrorism offences, and like Usman had been released early on licence after successfully appealing against his original indeterminate sentence.
Officers from the West Midlands Counter Terrorism Unit arrested the man after a search of his home address on Saturday.
The force has said that there is no information to suggest the arrested man was involved in the incident at London Bridge.
Khan, 28, was on licence and wearing an electronic monitoring tag when he launched the violent attack, which injured three others, after he was invited to the prisoner rehabilitation conference on Friday afternoon.
The attack has prompted the Ministry of Justice to review the licence conditions of every convicted terrorist released from prison, which the Prime Minister said was "probably about 74" people.
Speaking on Monday afternoon, the Prime Minister said he did not think Khan's sentence was "long enough in view of the gravity of his offence".
"In view of the view that was taken of him by the initial sentencing judge, Judge Wilkie, and looking at what the judge had to say about him it's clear he was viewed as a very serious threat," he told reporters.
Mr Johnson, told he had appeared more open to liberal ideas on law and justice in the past, said: "Look at my 2012 manifesto on crime ... I've campaigned for a long time for longer sentences for serious and violent offenders."
He added: "What I also think is you should try to rehabilitate people and you should try to change things where you can - I certainly believe in education in prison and I believe that's why we're putting £2.5 billion into prison, I want to try to turn people's lives around if you can.
"But you have to be realistic and what you must not have is a system of automatic early release and it was the automaticity that I'm afraid let us down here, because in the end the law had no choice but to let him out and then to hope that things would turn out well.
"I don't think that was a reasonable expectation given what we knew about him."
ITV News Correspondent Sejal Karia, who is at the vigil in Cambridge, has reported on the tributes that have been paid to Jack Merritt.
She tweeted that tributes to "the most wonderful human" have been paid by friends and family.
The family of Mr Merritt, from Cottenham, Cambridgeshire, asked for his death to not to be used to justify introducing "even more draconian sentences" on offenders in a heartfelt tribute released on Sunday.They said: "He lit up our lives and the lives of his many friends and colleagues, and we will miss him terribly.
"Jack lived his principles; he believed in redemption and rehabilitation, not revenge, and he always took the side of the underdog.
"We know Jack would not want this terrible, 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."
Ms Jones, a volunteer with the scheme from Stratford-upon-Avon, Warwickshire, was described as having a “great passion” for providing support to victims of crime by her family.
In a statement, they said: “She was intent on living life to the full and had a wonderful thirst for knowledge, enabling her to be the best she could be.
“Saskia had a great passion for providing invaluable support to victims of criminal injustice, which led her to the point of recently applying for the police graduate recruitment programme, wishing to specialise in victim support.”
Khan, who was living in Stafford, was given permission to travel into the heart of London by police and the probation service.
Convicted of planning to bomb the London Stock Exchange in February 2012, he was released from prison on licence in December 2018, halfway through his 16-year prison sentence.
He launched the fatal attack at an event held by Learning Together, a programme associated with the university’s Institute of Criminology, at Fishmongers’ Hall near London Bridge.
Armed with two knives and wearing a fake suicide vest, he was tackled by members of the public, including ex-offenders from the conference, before he was shot dead by police.
One of the three people injured in the attack has been allowed to return home while the other two remain in a stable condition in hospital, Met Police said.
No-one else is being sought over the attack.