Labour MPs must respect the mandate Jeremy Corbyn has been given by members, its new deputy leader Tom Watson has told the BBC’s Andrew Marr.
Few MPs backed Mr Corbyn in the leadership contest he has just won by a landslide – and high profile figures have refused to serve under him.
Mr Watson said he understood it was a huge change for MPs but the new leader wanted to build a broad-based party.
And there was “zero chance of a coup” against the new Labour leader.
He told those refusing to serve in the shadow cabinet: “There’s always someone else that can do a front bench job.”
Senior party figures such as Lord Mandelson and David Blunkett were among those warning that the party risked becoming unelectable without action to temper the new leader’s radical mandate.
Moderate Labour MPs have held “informal” talks about challenging Mr Corbyn when Parliament returns next week by organising a vote of no confidence,according to the Telegraph.
Mr Corbyn is expected to announce the first members of his shadow cabinet later.
Defeated rivals Yvette Cooper and Liz Kendall, shadow education secretary Tristram Hunt, shadow work and pensions secretary Rachel Reeves and shadow chancellor Chris Leslie, are among those who have said they will not serve under him.
Speaking on BBC Radio 5 live, leader of the Unite union Len McCluskey predicted Mr Corbyn would select a top team “drawn from all elements of the party”.
Mr Corbyn has been a marginal figure in the House of Commons for the past 32 years, and his policy programme, which includes scrapping nuclear weapons and renationalising utilities, is a major departure from recent Labour policy.
But his anti-austerity message and authentic image attracted Labour members and supporters who voted for him in their droves.
He won on the first round of voting in the leadership contest, taking 251,417 of the 422,664 votes cast or 59.1% – against 19% for Andy Burnham, 17% for Ms Cooper and 4.5% for Liz Kendall.
Tom Watson, who was elected as Mr Corbyn’s deputy, said he wanted a more “intellectually curious” approach to Labour policy and see the policy making process given back to members, as that was the only way to reconnect to communities they had lost.
But the former defence minister also suggested he had differences with Mr Corbyn over the new Labour leader’s desire to scrap Trident and take the UK out of Nato.
“I need to be honest about where I stand on things,” Mr Watson told Andrew Marr.
“I think Nato has kept the peace in western Europe for half a century, and Jeremy has said that – but he’s also said he’s worried about the eastern expansion of Nato, and I think he’s right to be cautious on that front.
“But we’ve got to work this out, you know, I’ve only been deputy leader for about 20 hours.”
Mr Watson said the party would have a debate about its policy on nuclear weapons.
Conservative minister Michael Gove, speaking on the Andrew Marr programme, congratulated Mr Corbyn who he said enjoyed a “very special sort of vindication” given the scale of his victory.
Asked if Mr Corbyn could win the 2020 general election, the justice secretary said: “Yes, and we have to face up to that reality.”
But he repeated Conservative warnings that, as a prime minister, Mr Corbyn would be a “real danger” to national security.
Prime Minister David Cameron tweeted: “The Labour Party is now a threat to our national security, our economic security and your family’s security.”