London:  Jeremy Corbyn has refused to stand by Britain's nuclear deterrent, giving his political opponents some relief from an otherwise depressing day on the campaign trail.

The Labour leader told a BBC TV audience there would be "no first use" of nuclear weapons on his watch, and several times dodged direct questions asking if he would use them in retaliation to a nuclear attack.

He did say their use would be "disastrous for the planet" and he did "not want to be responsible for the destruction of millions of people".

Foreign Secretary Boris Johnson leapt on Mr Corbyn's comments, saying they were "chilling".

"He was saying to the world, advertising that if it came to nuclear blackmail from Iran, North Korea or anywhere else that he would be vulnerable to that blackmail because he'd never press the button," Mr Johnson said.

The UK's £20 billion Trident nuclear deterrent would be "voided" under Labour, Mr Johnson said.

Mr Corbyn joined the Campaign for Nuclear Disarmament (CND) as a schoolboy in 1966 and was later their vice-chair. He is listed on their website as their vice-president for 2016/17.

His comments were a rallying point for Conservatives after yet another blow hit their campaign.

On Friday, a Conservative MP standing for re-election in Thursday's UK general election was charged with filing false election expense claims in 2015.

Mrs May also came under fire on Friday for her decision not to sign a joint condemnation from France, Germany and Italy of US president Donald Trump's decision to withdraw from the Paris climate achievement.

Mr Corbyn said "Given the chance to present a united front from our international partners [Mrs May] has instead opted for silence and once again subservience to Donald Trump.

"It's a dereliction of both her duty to this country and our duty to our planet."

Labour have been making hay with images from earlier in the year of Mrs May and Mr Trump holding hands during her visit to the US.

But Mrs May defended that decision in the evening TV appearance, when the two leaders took the stage one at a time to face audience questions. Mrs May said the UK was an independent nation and she had spoken to Mr Trump the night before, telling him the UK believed in the Paris agreement and didn't want him to leave.

On Friday morning, the Crown Prosecution Service announced it would charge three people with election offences.

They included the Conservative candidate for South Thanet Craig Mackinlay​, who could be sentenced to up to a year's prison if found guilty of declaring false election expenses in the 2015 general election campaign.

Mr Mackinlay narrowly beat Nigel Farage, then UKIP leader, in one of the tightest results in the 2015 election.

Police have been investigating whether a Conservative election 'battle bus' which visited constituencies had been properly declared under electoral laws. Last month they announced that no criminal charges would be brought against more than 20 other Conservative MPs over the battle bus campaigns.

Mr Mackinlay said in a statement on his Facebook page that "my campaign continues as before". "I am confident that I will be acquitted," he said. "Clearly this is a shocking decision by the CPS, given that I've done nothing wrong and I am confident that this will be made very clear as the matter progresses."

He also questioned the timing of the decision, asking "why leave this until a few days before the election".

Prime Minister Theresa May ended the day with a strong performance in the live TV encounter with a BBC studio audience. She pitched hard for the voters who had backed Brexit, telling them that if they voted Leave, they needed to make sure they got it.

And she denied she had called the election out of political calculation.

"I had the balls to call an election," she said. "I called a general election because I believe the British people have a right to say who they want to see leading them through the Brexit negotiations.

"They should have a prime minister who has an absolutely resolute determination to respect their will."

She repeatedly attacked Labour's "magic money tree" policies. But she suffered on questions about social care, particularly in response to a question from a nurse who said her payslips hadn't risen in almost a decade.

And she had a moment of embarrassment when she appeared not to know that UK aid money had gone to North Korea.