Nicola Sturgeon has questioned Boris Johnson's fitness to hold the office of Prime Minister after he claimed Friday's terrorist attack on London Bridge was the result of a decision by a "leftie government" - despite the family of one of the victims asking that his death not be used politically.
The First Minister said that those watching Mr Johnson's interview on the Andrew Marr programme this morning could not conclude he had the "seriousness, dignity, judgement or sensitivity" to be Prime Minister.
Writing on Twitter, Ms Sturgeon added that the interview had served only to answer the question of why Mr Johnson was "so desperate to avoid detailed scrutiny in this campaign".
Mr Johnson has not yet agreed to be interviewed by BBC journalist Andrew Neil unlike the other party leaders, and he also failed to appear on a Channel 4 leaders' debate last week.
However this morning he appeared on television to respond to Friday's attack which saw 28-year-old convicted terrorist Usman Khan, who was freed halfway through a 16-year jail sentence, shot dead after he stabbed two people to death and injured three others.
Mr Johnson said it was both "ridicuous" and "repulsive" that "individuals as dangerous as this man should be allowed out after serving only eight years" and that the government would now change the law.
Mr Johnson was emphatic in placing the blame for Usman Khan's release on Labour, saying: "His release was necessary under the law because of the automatic early release scheme under which he was sentenced, that was the reality, and that was brought in by Labour with the support of Jeremy Corbyn and the rest of the Labour Party.
"I opposed it both in 2003 and 2008, and now that I am Prime Minister I'm going to take steps to make sure that people are not released early when they commit... serious sexual, violent or terrorist offences."
He added: "The reason this killer was out on the streets was because of automatic early release which was brought in by a leftie government."
Yet David Merritt, father of one of the vicitms Jack Merritt, said his son's death should not be used to score political points, and Liberal Democrat candidate Chuka Umunna criticised both Labour and the Tories for "seeking to use a terrorist incident as a political football" amid the General Election campaign.
Khan was on licence and wearing an electronic monitoring tag when he attended a conference on prisoner rehabilitation hosted by Cambridge University scheme Learning Together at Fishmongers' Hall near London Bridge. Mr Merritt was the course co-ordinator of university's programme.
Armed with two knives and wearing a fake suicide vest, Khan was tackled by members of the public, including ex-offenders from the conference, before he was shot dead by police on London Bridge.
Footage posted online shows Khan being taken to the ground as one man sprays him with a fire extinguisher and another, reportedly a Polish man who worked at the Hall, lunges towards him with a narwhal tusk believed to have been taken from the wall inside the building.
In the wake of the attack, David Merritt said his son Jack was "a beautiful spirit who always took the side of the underdog." And he added that Jack "would not wish his death to be used as the pretext for more draconian sentences or for detaining people unnecessarily."
The attack has prompted the Ministry of Justice to review the licence conditions of every convicted terrorist released from prison, which is understood to be around 70 people.
Pushed on what is being done about them Mr Johnson added: "What we're doing there is we've taken a lot of action as you can imagine in the last 48 hours. I don't want to go into the operation details.
"I'm sure people can imagine what we're doing to ensure that 74 other individuals who've been let out early on the basis of this Labour change in legislation, they are being properly invigilated to make sure there is no threat."
Mr Johnson continued: "I do think there is an issue, as I have said, with automatic early release. I think it's wrong for serious sexual offenders, I think it's wrong for violent offenders, I think it's wrong for terrorists.
"So, I disagree with Jeremy Corbyn and Shami Chakrabarti when it comes to having shorter sentences."
Pressed on cuts to prison and probation services and the rising levels of assaults on staff during this time, he added: "That is why this new Conservative administration is putting £2.5 billion into our prison service."
Asked why this has not happened under the last years of Conservative government, he added: "I'm a new Prime Minister, we take a different approach."
However his Foreign Secretary Dominic Raab, who was on Sky's Sophie Ridge on Sunday programme, was asked about comments made by David Merritt and whether the governmnet was listening to him.
Mr Raab said: "Totally and no-one wants to see the politicisation of this." But he added: "I don't think after what we've seen both in this election and in the previous election, and in the individuals involved, that anyone would think taking the measures necessary to protect the public and putting their interests and their safety at the forefront, and as the over-riding priority, would be somehow politicisation.
"I think it's the necessary thing to do to keep people safe and it is only this Prime Minister and the Conservatives who are offering that."
Liberal Democrat foreign affairs spokesman Chuka Umunna criticised both Labour and the Tories. "Clearly the system needs to be looked at," he said: "But the facts are this. The assailant, the person who committed the acts here, was jailed under a regime inherited by the coalition government from a Labour government and then he was released early under a Conservative government.
"So, this happened under governments of different political persuasions."
Today Labour leader Jeremy Corbyn said that said he believed police officers had "no choice" but to shoot Usman Khan dead but that convicted terrorists should "not necessarily" serve their full prison sentence.
He said: "I think there has to be an examination of how our prison services work and crucially what happens to them on release from prison because I need to know whether or not the Parole Board were involved in his release, apparently they were not, they made that statement quite quickly after the release.
"Secondly, there were apparently no probation service involvement in monitoring this former prisoner who after all had only served half his sentence and he came out I think a year ago and there has to be an examination of what goes on in the prison because prisons ought to be a place where people are put away because of major serious offences but also a place where rehabilitation takes place."
Mr Corbyn said police were "stuck with a situation where there was a credible threat of a bomb belt around his body and it's an awful situation for any police officer, any public servant to be put in" as he backed the decision to kill the attacker.
A Sentencing Bill included in the Queen's Speech in October, which became defunct once the election was called, would have changed the automatic release point from halfway to two thirds for adult offenders serving sentences of four years or more for serious violence or sexual offences.
Judges can already impose extended sentences for offenders assessed as "dangerous", where they will serve two thirds, but the proposed legislation would make the longer jail terms mandatory for certain offences.
Mr Johnson said the automatice early release system had to end. "If you are convicted of a serious terrorist offence, there should be a mandatory minimum sentence of 14 years - and some should never be released.
"Further, for all terrorism and extremist offences the sentence announced by the judge must be the time actually served - these criminals must serve every day of their sentence, with no exceptions.
"These simple changes, in line with what I've been saying since becoming Prime Minister, would have prevented this attack. I believe they will help stop further attacks and these changes will be made urgently in the New Year if I am Prime Minister and have a majority in Parliament."
In August, Mr Johnson ordered an urgent review of sentencing policy, saying that dangerous criminals must be taken off the streets and punishments "truly fit the crime" if the public was to have confidence in the justice system.