Shadow chancellor John McDonnell has lashed out at opponents of Jeremy Corbyn, accusing them of trying to "destroy" the Labour Party in order to get rid of their leader.

Mr McDonnell said there was a "small group" within the party responsible for the current turmoil which has seen it beset by allegations of bullying, intimidation and abuse.

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His comments came after former shadow minister Seema Malhotra disclosed she had lodged a formal complaint with the Speaker John Bercow after staff working for Mr Corbyn and Mr McDonnell entered her House of Commons office without permission.

Speaking on the BBC's The Andrew Marr Show, Mr McDonnell challenged critics of the leadership to confront them directly and not to "pick on" staff who were not in a position to defend themselves.

"We have got to stop this now. There is a small group out there that are willing to destroy our party just to remove Jeremy Corbyn. We have got to stop them," he said.

"If you want to come for me and Jeremy that's up to you, but don't pick on staff who can't defend themselves."

Ms Malhotra said the unauthorised entry by staff into her office constituted a serious breach of parliamentary privilege.

"The implications of this are extremely serious. This is a breach of parliamentary privilege and is a violation of the privacy, security and confidentiality of a member of parliament's office," she told The Observer.

"Furthermore, my staff, including an intern, who have always been courteous and open, have felt harassed, intimidated and insecure, and decided themselves it would be best to not leave anyone alone in the office."

However, Mr McDonnell said the office manager concerned had simply been checking whether Ms Malhotra had moved out of the office after quitting as shadow chief Treasury secretary last month in protest at Mr Corbyn's leadership.

"I have now got a member of staff - she's a widow with daughters, this is her sole income - she's now worried she's going to lose her job and face prosecution because it's described as a break-in. That's just so distressing, it's unacceptable. This has obviously been an error," he said.

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But with the rift between the leadership and the party's MPs showing no signs of ending, Mr McDonnell acknowledged there would have to be some form of mediation once the current leadership contest is over.

"What we should do is do some mediated negotiations between the Parliamentary Labour Party, the NEC (national executive committee) and others, so we use the leadership contest to discuss the issues, but also we use it to help heal some of the wounds and bring it together," he said.

Mr McDonnell accepted that he and Mr Corbyn had made "mistakes" since winning the leadership last year and they would have to resign if they lost the next general election.

"That would be inevitable, wouldn't it? Every Labour leader who loses an election usually goes," he said.

Leadership challenger Owen Smith - the former shadow work and pensions secretary - said the party was on "its knees" and could split if Mr Corbyn remained at the helm.

"My grave worry is that the party might split apart, that having been a great force for good in Britain for a hundred years and more we could cease to be that," he told Sky News's Murnaghan programme.

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"We are not looking at the moment like a government-in-waiting. We don't look like a credible powerful opposition, one that people could imagine running the country. I think that's what we've got to be.

"It's time for Labour to really get up off its knees and start fighting back against the Tories. I know that's what Jeremy wants too but I'm not sure he can do that."