Dave Merritt, whose son Jack was one of two people killed by convicted terrorist Usman Khan, condemned the prime minister earlier this week for using the attack as justification for a series of tougher criminal policies.
Challenged on the remarks during the BBC leaders’ debate – just six days before the general election – the prime minister said he had “huge sympathy” for both victims’ families. “It was a terrible thing,” he said.
He added: "But I still think it's wrong that someone like Usman Khan who was sentenced 21 years or 16 years plus five on licence should have been out automatically on eight years."
The Labour leader described the attack last Friday – resulting in the deaths of 25-year-old Jack Merritt and 23-year-old Saskia Jones – as “utterly appalling”.
He went on: “I was very moved by what Jack Merritt’s father said about what his son was trying to do. That he wanted a society where you did address the huge problems where somebody committed awful acts like that - yes of course you must imprison them, yes you must rehabilitate them if you can.
He added: “We need security on our streets. Security doesn’t come on the cheap and if you cut the number of police officers… then we all pay a price with our own security.”
Following the London Bridge attack, the Conservatives vowed to toughen terror sentences and stop criminals entering the UK from the EU. They also launched a crackdown on people convicted of terrorism offences who had been released earlier.
But that prompted a furious response from Mr Merritt, who wrote in an article this week: “If Jack could comment on his death – and the tragic incident on Friday 29 November – he would be livid.
He added: “We would see him ticking it over in his mind before a word was uttered between us. Jack would understand the political timing with visceral clarity.
“He would be seething at his death, and his life, being used to perpetuate an agenda of hate that he gave his everything fighting against. We should never forget that. What Jack would want from this is for all of us to walk through the door he has booted down, in his black Doc Martens.
"That door opens up a world where we do not lock up and throw away the key. Where we do not give indeterminate sentences, or convict people on joint enterprise. Where we do not slash prison budgets, and where we focus on rehabilitation not revenge. Where we do not consistently undermine our public services, the lifeline of our nation."