Owen Smith called his Labour leadership rival Jeremy Corbyn “a lunatic” at a rally in west London.

Mr Smith was answering a question on how Labour could win back Tory voters and said: “At a hustings a few weeks ago, Jeremy Corbyn said, ‘Yes we’ve got to get some of the people who contemplated voting Tory in the past to vote Labour.’ Rubbish! We’ve got to get two million people who actually voted Tory, 12 months ago, to vote Labour, in 106 seats.

“And what you won’t get from me, is some, you know, lunatic at the top of the Labour Party, you’ll have someone who tries to form a coherent narrative about what’s wrong with Britain.”

Mr Smith also said he would fight a general election on a promise to keep Britain in the European Union if elected leader.

Almost all of the 106 seats Labour would have to win back from the Conservatives voted to leave the EU.

“Make party conference sovereign to make sure there won't be backsliding on the radical things I've promised,” Mr Smith said. “49 per cent of the people of this country didn't vote to leave the European Union. If we can win 49 per cent of the vote, we’ll be laughing.”

Mr Corbyn is firmly expected to win the competition, but Mr Smith said it was “50/50.”

“I’m telling you now, on the phones, this is 50 50 across the country. I was in Wolverhampton last night and we were winning hands down.

“There are 20 per cent of people who are undecided. I am telling you now at the end of this contest, I will have won it. “

Labour leadership contest: Jeremy Corbyn vs Owen Smith Show all 8 1 /8 Labour leadership contest: Jeremy Corbyn vs Owen Smith Labour leadership contest: Jeremy Corbyn vs Owen Smith Jeremy Corbyn and Owen Smith clash at a leadership hustings in Gateshead, where Mr Smith was scarcely able to answer a question without being booed by Mr Corbyn’s supporters PA Labour leadership contest: Jeremy Corbyn vs Owen Smith “Jeremy himself admitted he was seven out of 10 in terms of his faith in the European Union. He said it,” said Mr Smith during his second live debate with Jeremy Corbyn Getty Labour leadership contest: Jeremy Corbyn vs Owen Smith Ballot papers are currently due to be sent out on 22 August and returned a month later, with the result being announced at a special Labour conference on 24 September Getty Labour leadership contest: Jeremy Corbyn vs Owen Smith Jeremy Corbyn supporters cheer and wave placards as the Labour Leader addresses thousands of supporters in in Liverpool, England Getty Labour leadership contest: Jeremy Corbyn vs Owen Smith Labour Party leadership candidate Owen Smith poses for a picture with supporters during a picnic for young members in London Fields, Hackney in London Getty Labour leadership contest: Jeremy Corbyn vs Owen Smith The Labour leader has a spring in his step at a leadership rally in Sunderland Screenshot Labour leadership contest: Jeremy Corbyn vs Owen Smith Labour leadership contender Owen Smith delivers a speech at the Open University in Milton Keynes, where he promised to reverse Conservative cuts set to leave millions of low paid workers thousands of pounds a year worse off PA Labour leadership contest: Jeremy Corbyn vs Owen Smith Shadow Chancellor John McDonnell has urged Owen Smith to distance himself from those saying they want to split the Labour party Getty

One member said she would resign if Mr Corbyn won. Mr Smith told her: “If he wins, please don't resign, because we need to make sure we’ve got people fighting for our values to take on the Conservatives at the next election.”

Asked about his use of the word "lunatic" on BBC radio, Mr Smith later claimed he was in no way referring to Mr Corbyn.

He said: “I was saying that I wasn’t a lunatic. Having been accused earlier in the evening of running round like a lunatic, I was saying I wasn’t a lunatic.

“But if anybody is offended by the use of that word, then I do apologise. I’ve done that already this morning and I’ll do it again.

“But I wasn’t talking about Jeremy, I was talking about me.”

Mr Smith admitted that he was sometimes “colourful” with his language, but denied this was an impediment to him being leader.

A spokesperson for the Jeremy for Labour campaign, said:

"Owen Smith has degraded this contest by descending into personal abuse. He should apologise to people suffering with mental illness, many of whom would have been dismayed and upset to to hear such offensive language used in public by a Labour politician.