Jeremy Corbyn has accused the prime minister of politicising the death of London Bridge terror attack victim Jack Merritt by talking too soon about tougher sentencing for terrorists.

The Labour leader, who revealed he spoke to Merritt’s father, Dave, in the days after the student was killed, criticised Johnson for making a glut of statements about strengthening the law in the immediate aftermath of the atrocity.

Corbyn told the Guardian: “I deliberately tried not to politicise it. I simply said I think there are questions to answer about the way our prison service operates. The underfunding of the prison service, the role of the parole board and the role of the probation service.

“I think it’s right to ask those questions but not to leap to immediate conclusions. I think he did it far too much.”

Asked if Johnson politicised the Cambridge graduate’s death, he said: “I think he made too many statements too quickly about it all and I think it’s important to take stock of the situation.

“Obviously the first priority is to make sure everybody is safe of course.”

Corbyn said the killings of Merritt and colleague Saskia Jones by convicted terrorist Usman Khan was the lowest point of the general election campaign.

He spoke to the Guardian on the campaign trail before a rally in Birmingham, with the Tories ahead in the polls just a week before the election.

At the same time, his interview with ITV’s Julie Etchingham aired, in which Corbyn was pressed on whether he would return convicted terrorists on early release to jail.

“I think you have to investigate every case in which people have been given early release and you have to investigate all the circumstances surrounding the release of this particular individual and you have to also abide by the laws as well … It means looking at each case given early release and if there’s any cause for concern you recall them,” he said.

The Labour leader again apologised to those hurt by delays dealing with complaints about antisemitism.

“Antisemitism is a vile evil in our society. I am not a racist in any form. I’ve spent my life opposing racism. And I think the treatment of Jewish people that suffer from antisemitism is appalling. And where there’s been delays, by my party, in instituting a process, of course I apologise to those that suffered as a result of it,” he said.

In lighter parts of the interview, he was asked “the most romantic … wild and reckless” moment of his life, replying that he had enjoyed some “wonderful holidays” with his wife, Laura Álvarez.

Corbyn blamed his trailing personal poll ratings on “attacks in the media”, although he said he did not comment on opinion surveys.

On Thursday night, Labour escalated its ongoing complaint about BBC bias to the broadcaster’s director-general, Tony Hall. The party is unhappy about anti-Labour framing and the decision to allow the Conservative leader to “pick and choose” his BBC platform.

Andrew Gwynne, Labour’s co-campaign coordinator, raised the case of Boris Johnson’s failure to be interviewed by Andrew Neil despite the BBC giving the Labour party a “clear understanding that Boris Johnson had agreed the same terms”. Johnson also dodged a similar interview with ITV’s Etchingham.