Jeremy Corbyn and Theresa May have been involved in bitter exchanges as the political fallout from the London Bridge terrorist attack dominated the General Election campaign.
The Labour leader backed calls for the Prime Minister to quit over her record as home secretary when police numbers fell by almost 20,000, while Mrs May lashed out at Mr Corbyn over his opposition to counter-terrorism measures.
Mrs May also questioned Mr Corbyn's fitness to represent the UK in the crucial Brexit talks as she sought to return the focus of the election back onto the thorny issue of leaving the European Union.
Asked by ITV News if he backed calls for Mrs May to resign, Mr Corbyn said: "Indeed I would, because there's been calls made by a lot of very responsible people on this who are very worried that she was at the Home Office for all this time, presided over these cuts in police numbers and is now saying that we have a problem - yes, we do have a problem, we should never have cut the police numbers."
His comments came after Steve Hilton, a former adviser to David Cameron in Number 10, said Mrs May was "responsible for security failures" and "should be resigning, not seeking re-election".
The Labour leader later clarified his views, stressing it was a matter for the electorate whether to oust Mrs May: "I'm not backing away from anything, what I'm saying is there's an election on now there's a choice before everybody.
"I'm articulating what is a deep anger amongst those people that have seen 20,000 police officers lose their jobs, seen firefighters lose their jobs, seen ambulance crews unable to cope.
"(Mrs May) needs to think about what she did while she was home secretary."
Liberal Democrat leader Tim Farron accused Mrs May of failing in her duty to keep the UK safe.
He told the Press Association: "On one of the most important tests facing us as a country - security - Theresa May has failed as both Prime Minister and home secretary. She has failed by cutting police numbers.
"She has made poor choices. She has chosen to give away a corporation tax cut to the biggest and wealthiest businesses in our country, multi-nationals, instead of spending that money on keeping us safe and backing the police force and security services.
"Cutting police numbers is the most sure way of keeping us less safe."
But Mrs May defended her record as the Tories hit out at Labour over Mr Corbyn's record on tackling terrorism.
The Conservative Party's official Twitter account said "the shoot-to-kill policy saves British lives - Jeremy Corbyn opposes it".
Mr Corbyn insisted his comments on shoot-to-kill had been taken out of context and he backed the police to take the "necessary action" where lives were at risk.
He said: "What I said was that I wanted our police to be able to act in a defensive capacity. I don't want anybody, nobody wants police going out shooting people.
"They don't want to do it, nobody wants to do it. In the situation that they were faced (with) at the weekend or faced in Westminster, they took the necessary action."
Facing repeated questions about her record after a speech in London, Mrs May said: "I have been responsible for giving the police extra powers to deal with terrorism.
"Jeremy Corbyn has boasted that he has opposed those powers and opposed the powers for anti-terror actions throughout his time in Parliament.
"And I also support, absolutely, shoot-to-kill and I think what we saw on our streets on Saturday was how important that was."
She said that since 2015 police budgets had been protected "despite the fact that Jeremy Corbyn's front bench suggested that police budgets should be cut by up to 10%".
In a speech at the Royal United Services Institute, where she had launched her campaign for the Tory leadership just under a year ago, Mrs May accused the Labour leader of failing on Brexit.
"Jeremy Corbyn seems to think that any deal - no matter what the price, no matter what the terms - is better than no deal," she said.
"The bureaucrats in Brussels would think Christmas had come early if the British government adopted such an approach."
She also hit out at Mr Corbyn's economic plans, claiming they would mean "punishing" families and businesses.
The business tax plan was "not leadership" and while it made "a good soundbite for an election" it would be "a disastrous policy for our country".