Jeremy Corbyn called for Theresa May to resign as Prime Minister over cuts to police numbers as the political fallout from the London Bridge terrorist attack dominated the General Election campaign.
The Labour leader's comments came as Mrs May's record as home secretary, when police numbers fell by almost 20,000, was under the spotlight following the second terror attack during the election period.
But Mrs May defended her record in office and accused Mr Corbyn of failing to support measures to tackle terrorism.
She sought to turn attention back to Brexit with a personal attack on the Labour leader's fitness to represent the country at the forthcoming negotiations with Brussels.
Mr Corbyn conceded that Thursday's General Election was "perhaps the best opportunity" to remove the PM from her post, but, asked by ITV News if he backed calls for Mrs May to resign, he 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 of London Bridge, Manchester, Westminster Bridge" and "should be resigning, not seeking re-election".
The Prime Minister used a campaign speech in London to focus on Brexit and the economy, but was repeatedly pressed over whether she would reverse the cuts to police numbers since 2010.
Mrs May 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%".
She added: "It is also about the powers you give to the police and 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."
In her speech, Mrs May insisted that Brexit "remains the most critical issue in this campaign" and "the question of leadership" was at the heart of the contest.
She said Mr Corbyn was "not fit to negotiate a good Brexit deal for Britain".
In a speech at the Royal United Services Institute, where she had launched her campaign for the Tory leadership just under a year ago, she said: "Jeremy Corbyn seems to think that any deal - no matter what the price, no matter what the terms - is better than no deal.
"That's not leadership. That's an abdication of leadership.
"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".
In an interview with the London Evening Standard, Mrs May said there was a new phenomenon of "terrorism breeding terrorism".
She told the paper: "You have had the well-planned terrorist attacks in the past, and you have had the lone wolves. Now, we see this terrorism copying others, using crude means to attack us and do us harm."
Mrs May said the "pace of intent to try to do us harm has been significant" and that the threat had become "more complex".
She also claimed that society had to be "more willing to call out terrorism and extremism" having been "too tolerant".
Mrs May was asked whether she would recognise those who helped in the Manchester and London attacks in the Birthday or Christmas honours, but said "we never talk about those things".
"What I will say is that we are making sure that we identify acts where police and others have really given people help and support and shown bravery in this incident."
Asked about Mr Corbyn's call for her to quit, Mrs May said: "On Thursday the people of the UK have a very simple choice when they come to vote.
"It is about who they believe has the leadership to take this country forward, to get the best Brexit deal for Britain from Europe, to ensure that we can build that stronger, fairer and more prosperous Britain for the future."
On the campaign trail in Edinburgh she said: "Who has the leadership, who has the vision who has the plan?
"It's me and the Conservative Party that have that leadership, have that plan and have that vision and that will take this country forward for the future."