Theresa May and Jeremy Corbyn were forced to defend their records as they faced a live TV grilling.
The UK Prime Minister came under fire from members of the studio audience over her cuts to public services and her plans for social care.
Mr Corbyn faced questioning on his attitude to security issues and past comments about the IRA and the Falklands War.
Appearing on a Sky News/Channel 4 "Battle for Number 10" broadcast, the Labour leader refused to be drawn on whether he would authorise a drone strike against a terrorist plotting overseas to attack the UK.
"It is a hypothetical question," he said. "We have to look at the evidence that is there at the time to make that fatal decision one way or the other."
Mr Corbyn, a lifelong opponent of nuclear weapons who has made clear that he would never authorise their use, nevertheless indicated he would issue the customary final instructions to the commanders of the Trident submarine fleet if he became prime minister.
"I will write the appropriate letter to our commanders who are obviously very responsible, very loyal naval officers," he said.
During her grilling from the studio audience, Mrs May was accused by a police officer of presiding over "devastating" cuts, asked by a midwife to justify her "chronic underfunding" of the NHS and heckled over school funding.
The Prime Minister insisted that she was determined to do the right thing for the country, referring to her reputation as a "bloody difficult woman".
"Doing what is the right thing by the country. Sometimes you have to be difficult in order to do that," she said.
"We need to have a government that is open about these things and is willing to find ways of addressing them.
"If in order to address them and do the right thing by the country, it takes being a difficult woman, then that's exactly what I will be."
Mrs May also reaffirmed that she would walk away from the forthcoming Brexit negotiations without a deal rather than accept a "bad" deal.
"I think you have to. In negotiations you have to recognise that you're not in there to get a deal at any price."
Under the format agreed by the two parties, the two leaders each faced 20 minutes of questions from the audience with a further 18 minutes in front of interviewer Jeremy Paxman, with Mr Corbyn going first.