Labour leadership race: Jeremy Corbyn and Owen Smith clash in bitter first head-to-head debate

The challenger was heckled and booed by members of the audience in Cardiff

Bitter in-fighting within the Labour Party was cast into the open as Jeremy Corbyn and Owen Smith clashed in the first head-to-head debate of the leadership campaign.

Mr Smith, who pledged to deliver the most radical programme since the Labour Government of 1945, suffered a bruising encounter in Cardiff as he was heckled and booed by members of the audience when he mentioned the “disunity” in the party's ranks. One audience member shouted “you split this party!” while another simply added: “Nice suit”

In an attempt to calm tensions Mr Smith at one point directly addressed the audience and said: “We are not behaving like comrades to each other.”

While the two contenders echoed each other’s sentiments on curtailing bankers’ bonuses, tackling tax evasion and investing billions in infrastructure, they clashed on the renewal of Trident. Mr Corbyn, a lifelong critic of the nuclear deterrent, was greeted with one of the loudest cheers of the evening when he reminded the audience he had voted against its renewal just weeks ago. Nuclear weapons are the “ultimate weapon of mass destruction which indiscriminately kills” Mr Corbyn claimed.

Mr Smith, who repeatedly referred to himself as a Bevanite, said: “I'm in favour of a world without nuclear weapons, I'm in favour of the Labour Party being in the vanguard of looking for multilateral disarmament.”

But he added: “I believe the world has become a more dangerous, volatile place, I believe Russia is a more dangerous power than it used to be.

”And my view about this is very clear, that we must retain a nuclear deterrent in order to enable the multinational disarmament of the entire world arsenal. That is the unfortunate, terrible truth.“

In the heated 90-minute debate in Cardiff the pair clashed as Mr Smith acknowledged that “we agree about so much of this stuff”, with Mr Corbyn swiftly retorting: “So why did you resign?”

Mr Smith replied: “Because I don’t think you’re going to be able to deliver it. I don’t think we can win with Jeremy at the moment. And without being able to win and put our principles into practice, I don’t see that we are going to be able to do anything other than protest. We’ve got to win in order to get this stuff done, otherwise it’s just hot air”.

Looking at his challenger, the Labour leader responded: “You walked away. You walked away”.

The Labour leadership candidates took part in a heated debate in Cardiff (Matthew Horwood/Getty Images) (Getty)

There were divisions over Labour's approach to Brexit, with Mr Smith leaving little doubt that he blames Mr Corbyn for his lacklustre campaigning in the European Union referendum. He said that the Labour leader should have been “in the vanguard” of the EU referendum campaign and told Mr Corbyn: “We should have been absolutely in the trenches fighting every day and I don't think we fought hard enough.”

Mr Corbyn's call on the day after the poll for the withdrawal process to begin immediately had effectively “allied ourselves to the Tories” he said. But Mr Corbyn insisted: “We spent a lot of money on it, we did a lot of campaigning. I travelled the whole country doing a very large number of meetings.”

He also dodged Mr Smith's repeated challenges to join him in demanding a second referendum on any Brexit deal, saying only that it was likely to be an issue in the general election. Mr Corbyn said that “the result is what the result is”, adding: “We have to make the best of it.”

It is clear that Mr Smith, who is relatively unknown outside the Parliamentary Labour Party, has the most to gain from the televised debates. But speaking to The Independent, 71-year-old Julie Williams, a Labour Party member in the audience, said she was unsure who to vote for before the debate. When the event came to a close, she had made her mind up - she’ll be voting for Mr Corbyn when the ballot papers are sent out later this month. Her 68-year-old husband, Richard, however, remained unconvinced. “Jeremy is good at convincing people in this audience,” he said. “But most of us are well off here… his challenge is to convince the people out there.”

The event, held just miles from Mr Smith’s constituency, is the first in a series of debates Labour has organised across Britain during the leadership contest. So far, events have been confirmed in Cardiff, Gateshead, Nottinghamshire, Birmingham, Glasgow and London.

Lousie Haigh, who remains a minister in Mr Corbyn’s shadow Cabinet but is backing Mr Smith for the leadership, told The Independent shortly after the debate finished that she thought Mr Smith was “fab”.

“I thought Owen set out very clearly, very credible policies that he has. He’s come out with more policies in the last two weeks… than we have had in the last ten months,” she said.

Ms Haigh added: “I think most people that came today had already made their mind up about who they are supporting. I think probably the room was towards Jeremy… 200 members are not representative at all. The vast majority who voted Jeremy last year are undecided.”

Earlier on Thursday the incumbent leader outlined 10 pledges to “rebuild” and “transform” Britain - a day after Mr Smith laid out programme of reform which he said would amount to the “biggest boost to living standards for a generation”. In a speech in Dagenham, east London, Mr Corbyn vowed to inject £500 billion of investment into public services. The leader added, under a Labour government, one million homes would be built, including at least 500,000 council homes.

“A new £250 billion national investment bank, backed up with a network of regional development banks, will put power to determine their own futures back into the hands of those places outside of Westminster and the City of London,” he added.

It comes after John McDonnell, the shadow Chancellor and the Labour’s leader’s closest political ally, said “Owen Smith’s friends” were using the possibility of a damaging separation to drive votes towards their chosen candidate. He added that anti-Corbyn MPs organising around the challenger’s leadership campaign are holding the party to ransom under the “threat” of a split.

Mr McDonnell also repeated his calls from Mr Smith to denounce the threats of a split. The result of Labour’s leadership contest will be announced on 24 September at a special conference.