The campaign to elect the leader of one of Britain's most powerful trade unions in 2003 was tarnished by malpractice, fraud and misuse of members' money, according to allegations in a 1,000-page report.
Supporters of Kevin Curran, who subsequently resigned as general secretary of the GMB union, broke rules by accepting material help from employers and a firm of solicitors - evidence supplied to the investigation alleged.
Details of the accusations have been supplied to the union's national executive and will be made public on Saturday at an emergency conference of the union.
A lawyer representing Mr Curran said there had been allegations of similar improprieties against the present acting general secretary, Paul Kenny, during the same election, but they had not been investigated.
A report, drawn up by Phil King of Thompsons solicitors, alleges that full-time officers and staff of the union distributed Mr Curran's election campaign material when they should have been working on behalf of members.
Mr Curran's supporters are accused of breaching union rules, which forbid active campaigning at election times, and using the GMB's money partly to pay for the production and postage of literature.
It is thought that the money was used to finance the secondment of a TUC official to the GMB, who then worked on Mr Curran's campaign. The TUC has said that it played no part in the election.
An official complaint about the alleged abuses was made to the GMB's election committee in the Lancashire region, but the allegations were instantly rejected. Mr King believes the national executive might have ordered a fresh election if there had been a proper investigation.
A northern firm of solicitors was said to have supplied staff to process at least 2,000 pro-Curran letters and allowed his supporters to use its call centre free of charge to contact those who might vote for Mr Curran.
The solicitors also allegedly opened and co-signed a "Friends of Curran" bank account to pay campaign expenses. The investigator had no access to the account because of the Data Protection Act.
Debbie Coulter, Mr Curran's running mate, told the inquiry that he had informed her that he was funded by outside groups, including employers.
Louise Christian, the lawyer representing Mr Curran, said that an independent inquiry into the allegations, under John Hand QC, had been scrapped as soon as he stepped down as general secretary.
She said he did not accept that the investigation was "fair or impartial" and would seek notice of the detailed allegations so that he could respond to them.
Responding to Ms Christian's remarks, a spokesman for the union insisted that the investigation was independent and that all allegations were investigated.
"Mr Kenny co-operated fully with the inquiry," he said. "Mr Curran was offered numerous opportunities to assist the investigation, but he declined to do so."Reuse content