One of Jeremy Corbyn's closest allies has called on Labour MPs to rally behind the "new politics" of the party leader amid speculation of a New Year purge of his shadow cabinet critics.
John McDonnell, the shadow chancellor, acknowledged that Mr Corbyn's election as Labour leader had been a "massive cultural shock" to many MPs, but insisted "there is no going back" on the course he had set.
His comments came amid a series press 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 that they did not comment on reshuffles.
However after a tumultuous week - which laid bare the 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 in the face of a threatened shadow cabinet revolt, he still saw the majority of his top team and the majority of Labour MPs vote with him in opposing military action.
He was then further 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.
"Now Jeremy Corbyn's leadership has been strengthened," said Mr McDonnell, writing in The Observer .
"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 among the figures reportedly 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 insisted the party would not tolerate such behaviour but at the same time he rebuked those who sought to "make mischief" by "misreporting or misrepresenting" what was happening.
He made clear that Mr Corbyn remained determined to re-make the party in his own left-wing image and that of the grass roots activists who propelled him to the leadership.
"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."