Left-wing activists will not force out Labour MPs - John McDonnell
Moderate Labour MPs must "come to terms" with the party's new direction but there is "no way" left-wing activists will be allowed to force them out, John McDonnell said as he played down the threat of a leadership challenge.
The shadow chancellor dismissed concerns that internal critics could face an organised campaign to have them deselected in favour of more radical candidates.
And he said a threat by leading anti-Corbyn MP Simon Danczuk to seek to force a contest if the party performed poorly at devolved and local elections in May was "Simon being Simon".
Concerns have been raised by some that the creation of the Momentum campaign group of so-called "Corbynistas" drawn to the party by anti-austerity and other leftist policies will act to "purge" those to the right.
Some have already faced local petitions demanding their removal.
Veteran MP Frank Field warned any such move could be met by a mass rebellion - with MPs backing their ousted colleagues in a by-election in defiance of party rules.
But Mr McDonnell told BBC1's Andrew Marr Show. "We are opposing any threat to individual MPs. We are not in favour of reselection.
"The democratic processes in the Labour position will take place in the normal way.
"There is no way we will allow MPs to be deselected in that way. We will work together on this."
Mr Danczuk told newspapers he could stand as a "stalking horse" challenger to open the door to more established colleagues such as Chuka Umunna, Dan Jarvis and Emma Reynolds to mount a challenge and "give us some chance of winning the next general election".
In the latest of a series of highly critical articles about Mr Corbyn in the Mail on Sunday, Mr Danczuk said he was guilty of "a profound lack of judgment and naivete".
"He is unsuited to leading a major political party and the sooner we get a Labour leader who is, the better."
Mr McDonnell said: "That is Simon being Simon isn't it? There will be people who have to come to terms with the change and they will do it slowly but they will."
Under Labour rules, potential challengers to a sitting leader must secure the support of 20% of MPs - at present 46 of 231 - to force a contest.
But any challenger who got on the ballot paper would face a stiff test given the dramatic margin of Mr Corbyn's victory in September, especially among the tens of thousands of new party recruits enthused by his anti-austerity message.
Mr Danczuk's latest broadside against the leadership came as Ed Miliband's former policy chief Jon Cruddas announced he was forming a new group aimed at ensuring the party builds "a broad coalition of support".
"The country needs a Labour party capable of boldness, but absolutely clear that what matters is building a broad coalition of electoral support. We didn't do that in 2010 and we ignored it in 2015," he wrote of Labour Together in The Guardian.
"Jeremy Corbyn has rightly challenged the party to rethink the way in which it does politics. This is a challenge we wholeheartedly embrace."
Mr McDonnell said: "We are radicalising the parliamentary party already.
"People are becoming involved in that debate and they are going back to their constituencies and they are being accountable to the new membership as well as the old membership."
Mr Field - who successfully fought off a deselection attempt by the left-wing Militant group in the 1980s - told BBC1's Sunday Politics: "There will be a large group I would hope of MPs who will, if colleagues are unfairly treated, encourage their colleagues to stand in by-elections, stand as 'Independent Labour' candidates and then a large number of us, including me, would go and campaign for them.
"It is capital offence to campaign for somebody standing against an official Labour candidate but if enough of us go, they can't pick us all off and expel the lot."
Ken Livingstone - the maverick former left-wing Labour MP who served two terms as mayor of London - said MPs who regularly defied the party whip should expect to face challenge.
He said it was "inevitable" that MPs would have to shift to the left.
"We should see a party more in Mr Corbyn's image," he told Sunday Politics.
"The parliamentary party is significantly to the right both of the rank-and-file and the leadership."
Most MPs would "engage with new members, they will moderate their criticisms of Jeremy Corbyn if he is seen to be doing quite well", he suggested.
But he went on: "If you have a thousand new members joining your party because they supported Jeremy Corbyn's policies and you have an MP completely undermining him ... they should have the right to challenge that.
"I was challenged by my local party because they thought I was too left wing. They had the right to do that.
"It should not be a job for life."
Labour MP Jess Phillips said she would join Mr Field in backing deselected MPs in a by-election.
"If I thought someone had been genuinely picked off unfairly - then yes I would go and help them," she told BBC Radio 5's Pienaar's Politics.
"In principle if I thought someone had been wronged I'd stand up. I t entirely depends on the circumstances, but the party isn't always right. The party isn't also unilateral. It's lots and lots of different people."