Keir Starmer has claimed Labour is "united" as he faced accusations of purging left-wing candidates from standing at the next election.
It comes after a dossier compiled by left-wing figures claimed the Labour leader is attempting to "erase the Left from public life".
In recent months several individuals, including the ex-MP Emma Dent Coad, have been stopped from standing as parliamentary candidates.
On a visit to Imperial College London on Monday, the Labour leader, however, claimed the party was "united" ahead of the next general election.
He appeared to reject allegations of a purge of left-wing candidates, arguing instead that he wanted to build a "team for the future".
He told broadcasters: "We are preparing for the next election, the sooner the better.
"I am determined to have a team of incoming MPs, who are the team for the future.
"We will have a big challenge and so of course we are making sure we have got the very best candidates to put before the public for that general election which we so desperately need."
Last month the former MP for Kensington Ms Dent Coad said she was "devastated" after being blocked from standing as a parliamentary candidate in her old seat.
The former Shadow Chancellor John McDonnell said it was "one of the most disgraceful acts I have witnessed" in his 50 years as a Labour member.
The dossier, which mentions Ms Dent Coad, also cites Maurice Mcleod, who was blocked from standing in Camberwell & Peckham - despite union backing.
The safe Labour seat will be vacated at the next general election when the party's former Deputy Leader Harriet Harman resigns.
In a statement in October, Mr Mcleod said he was "blocked by the party machine" and hit out at the "unfair decision taken behind closed doors".
The document also highlights that a third prospective candidate and trade unionist Lauren Townsend was also prevented from standing in Milton Keynes North.
The dossier claimed no rules have been cited for the blockings and "merely concerns about 'due diligence'" including social media posts.
It said selections have always been "politically contested" with "bureaucratic manoeuvres from the leadership, but this is on another scale entirely".
A Labour source told The Mirror: "It’s right that the Labour party expects prospective MPs to uphold the highest standards. Under Keir’s leadership that’s not going to change”
