Media playback is unsupported on your device Media caption "If anyone is perpetrating abuse, they should be kicked out of the party" - John McDonnell, Shadow Chancellor

Some of Jeremy Corbyn's critics are willing to destroy Labour in order to remove him, John McDonnell says.

The shadow chancellor said "a small group of people" were responsible for the turmoil in the party.

He spoke as a new row broke out over "unauthorised access" to the office of ex-frontbencher Seema Malhotra.

Ms Malhotra has formally complained to the Speaker, saying Mr McDonnell and Mr Corbyn's staff violated the privacy of her Westminster office.

Mr McDonnell said his office manager thought the premises were no longer occupied, and accused Mr Corbyn's critics of picking on members of staff.

BBC political correspondent Chris Mason said the spat mattered because it played into the wider row about claims of intimidation in the party's ranks.

Media playback is unsupported on your device Media caption "I have reason to believe there has been unauthorised access to my office" - Seema Malhotra, MP

Ms Malhotra, who resigned as shadow chief secretary to the Treasury last month in protest at Mr Corbyn's leadership, has complained about two officials - one working for Mr Corbyn and another who works for Mr McDonnell.

She said there had been unauthorised access to her office "on more than one occasion", saying she had "no idea" why they went in and that the incident raised "fundamental questions" about the "security and safety" of her staff.

In her letter to Commons Speaker John Bercow, she said her staff had felt "harassed, intimidated and insecure".

Speaking on the Andrew Marr Show, Mr McDonnell - who had been Ms Malhotra's boss in Labour's Treasury team - said his office manager had spotted a pile of boxes outside her office a month after she resigned and assumed that office was empty.

He said the member of staff, who was worried about losing her job, had apologised to Ms Malhotra's team and that he had not been told about the incident before the formal complaint to Mr Bercow was lodged.

Turning directly to the camera in his BBC interview, he appealed to the party to "stop this now".

"There's a small group out there that are willing to destroy our party just to remove Jeremy Corbyn," he said.

"We have got to stop them."

It was "fine" for them to target the leadership, he said, "but don't pick on staff who can't defend themselves".

Analysis

By BBC political correspondent Chris Mason

The substance of the allegations made by Seema Malhotra - and the credibility of the denials by Jeremy Corbyn and John McDonnell - can't be independently verified.

But what they highlight, again, is important: the toxic atmosphere at the heart of the Labour Party.

As if to prove that further, here are some of the words used privately by those on either side of this argument to me this morning:

"Inaccurate."

"Depressing."

"Cheap."

"Smear."

"Pathetic."

And then remember that these are words being used by people in the same party, who are meant to be united by the same aims: being Her Majesty's Official Opposition now and aspiring to lead the country after the next election.

Mr McDonnell predicted Labour MPs would accept the result if Mr Corbyn retained the leadership, saying most of them "just want to get on with the job".

He also acknowledged he and Mr Corbyn had made mistakes in their Labour leadership and said they would resign if Labour lost the next general election.

Ms Malhotra's replacement as shadow chief secretary, Rebecca Long-Bailey, told Sky News staff had been planning to swap their offices and thought Ms Malhotra had already vacated hers.

On realising Ms Malhotra was still based there, the member of staff "walked straight back out of the office again and left", Ms Long-Bailey said.

She added: "Unfortunately there has been a bit of miscommunication and misunderstanding on both sides."

Media playback is unsupported on your device Media caption Owen Smith says that it has been "absolutely heartbreaking" to see the levels of abuse within the party

The row comes after more than 40 female Labour MPs wrote to Mr Corbyn, saying he had failed to do enough to prevent "disgusting" threats against members.

Speaking on Saturday, the leader condemned abuse among members, saying "it has no place in our party".

He said: "I don't do personal abuse, I don't respond to personal abuse, I condemn any abuse from others."

Mr 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.

He told Sky News: "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."

Mr Smith has also said his wife, Liz, had been a victim of online abuse and claimed there was now a level of abuse, anti-Semitism and misogyny in Labour that was not there before Mr Corbyn became leader.

"My wife stood recently for a community councillor position in the village where we live in South Wales and was subject to a torrent of online abuse. It's a community council position."

He added: "I think it's just absolutely unacceptable."

The winner of the leadership contest will be announced on 24 September.