Len McCluskey has condemned as “vicious lies” the allegations made against Unite activists during last weekend’s Young Labour election.

He spoke out after the Labour Party launched an official investigation into some Young Labour members. The probe, led by former Labour leader in the Lords Jan Royall, will look at the election of a youth representative for the NEC, won by Jasmine Beckett on a slender margin, amid accusations of intimidation from both sides, as well as the row over alleged anti-Semitism in the Oxford University Labour Club

One of the allegations made is that Unite delegates at the Young Labour conference in Scarborough were bullied into supporting James Elliott, the losing candidate. However, Unite general secretary McCluskey has described the claims as part of “an organised assault” on the “integrity” of young members of the union. He said the disagreement was part of a wider “quest to undermine the Labour leadership.”

“On behalf of Unite I want to put on record how proud I am of our young members, and the professional way that they have conducted themselves during the Young Labour elections and conference,” he said

“The dignity displayed when subjected to vicious lies and an organised assault on their integrity is tremendous. They put to shame those in our party whose conduct has been nothing short of disgraceful and confirm once again that some in our midst will stop at nothing, including destroying the reputation and hopes of our party’s young activists, in their quest to undermine the Labour leadership.”

He also confirmed that Unite would begin its own investigation into the election, focussing on whether any of the trade union’s rules were broken.

“Unite will conduct its own inquiry into whether union rules were broken but we remain firmly of the view that the case for a full, independent inquiry into the practices of Young Labour and the weekend’s election grows stronger by the minute. The party general secretary must now act to restore faith and trust in Young Labour.”

Writing for LabourList, Beckett said that the conference “was not […] our movement at its best”, and claimed that delegates were subjected to “outside interference”.

“Factionalism, grievance and outside interference from people who were neither young nor delegates made it difficult for too many,” she wrote. “This has got to stop.”

Today young Unite members who attended the conference released a statement defending the actions of the union’s activists. It said: “Delegates unanimously agreed that they would hand the Unite ballot that they had been allocated by party staff, each representing the votes of 50,000 dues paying members of Unite, to be cast into the ballot box by the delegation leader once they had put the cross by James Elliott.

“There were no objections to this practice and indeed it is standard practice for trade unions using their votes at Labour Party conferences.

“We were each mandated to cast these votes for James Elliot by Unite’s National Young Members’ Committee which had overwhelmingly voted to endorse him as youth representative on the National Executive Committee of the Labour Party.”

It adds that “one delegate went back on his word and left the venue with the Unite ballot paper that he had been allocated by the Labour Party staff and refused to allow the delegation leader to see it and ensure that Unite’s mandate was fulfilled.”

Last night a spokesman for Labour confirmed details of its inquiry, saying: “The Labour Party takes all allegations of anti-Semitism, racism, bullying, intimidation and candidate misconduct very seriously. Baroness Jan Royall is currently leading an investigation into the conduct of individual Young Labour Party members. Baroness Royall will consider all allegations and all relevant evidence.”