John McDonnell, the shadow chancellor, admitted that Mr Corbyn’s election as Labour leader had been a “massive cultural shock” to many MPs, but he insisted “there is no going back”.
His comments came amid reports suggesting that Mr Corbyn is preparing a clear-out of critics who defied him over bombing Syria in a shadow cabinet reshuffle early in the New Year.
Labour sources would not be drawn on the reports, saying they did not comment on reshuffles.
But after a week which exposed deep divisions within the party, Mr Corbyn is widely seen to have emerged with his position strengthened and may feel emboldened to act.
Despite being forced to grant a free vote in the Commons debate on Syria because of a threatened shadow cabinet revolt, he still saw most members of his top team and the majority of Labour MPs vote with him in opposing military action.
He was then bolstered by a better-than-expected Labour victory in the Oldham West and Royton by-election which saw the party see off the challenge of Ukip with an increased share of the vote.
Mr McDonnell, writing in The Observer, said: “Now Jeremy Corbyn’s leadership has been strengthened. The message is clear: unite around the principles of the new politics and we can be the most powerful force for progressive political change in generations.”
Chief whip Rosie Winterton, shadow defence secretary Maria Eagle, shadow culture secretary Michael Dugher and shadow Northern Ireland Secretary Vernon Coaker are reportedly among the figures who could be vulnerable if Mr Corbyn does move against the dissenters.
The reports are likely to heighten concerns among Labour moderates who have complained of orchestrated online bullying and abuse from Corbyn supporters with threats of de-selection. Two MPs have reported death threats to the police.
Mr McDonnell said the party would not tolerate such behaviour but at the same time he rebuked those who sought to “make mischief” by “misreporting or misrepresenting” events.
He made clear that Mr Corbyn remained determined to re-make the party in his own left-wing image.
“The new leader was also elected with an overwhelming mandate on a political programme that seeks to take the party in a direction that reflects the current views of party members,” he wrote.
“This platform explicitly seeks to transform the party from the traditional centralised party into something more akin to a mass social movement, responding to the rising demand for greater activist engagement.”
He added: “People realise that if Labour is to fulfil its founding goal of transforming our economic and political system into a more equal, free and truly democratic society, which provides security and life-changing opportunities to the British people, then there is no going back.”
Meanwhile, former shadow cabinet minister Tristram Hunt has urged Mr Corbyn to pull out of a fundraising dinner for the Stop the War coalition on Friday, telling BBC1’s The Andrew Marr Show the group had picketed the Labour headquarters when the party was trying to run a phone-bank for the Oldham by-election.
“We have also seen some pretty ugly comments from them about Hilary Benn and the fact that Hilary Benn should be sacked. Also their comments about Islamic State, their comments about how the French almost had it coming to them.
“They are a really disreputable organisation,” he said.