Desperate attempts were allegedly made to conceal the involvement of a senior minister in the campaign to re-elect Sir Ken Jackson as leader of the Labour Party's biggest financial donor. The campaign subsequently failed after allegations of vote-rigging.
Amid "concern from No 10", Sir Ken expressed anxiety that revelations about the participation of the Transport minister John Spellar in the nominating process at the Amicus-AEEU union would be seriously damaging, according to a legal submission.
There is no suggestion that Mr Spellar took part in or knew of electoral malpractice. However, the minister was one of Sir Ken's closest advisers.
Officials at the union have admitted they voted more than once to nominate Sir Ken in his unsuccessful campaign to remain as general secretary beyond his 65th birthday.
Mr Spellar is known to have donated £30 to Sir Ken's campaign. The eventual victor, the left-winger Derek Simpson, subsequently urged Tony Blair to stop the minister "meddling" in the union.
Last night a source close to Sir Ken insisted that Mr Spellar was not heavily involved in the leadership campaign. "He voted in his branch and that's about it," the source said.
The papers allege that after the "double-voting" was exposed by The Independent, Sir Ken put the malpractice down to "over-enthusiasm" and admitted that he had probably done something similar himself over the years.
The accusations appear in a submission to an employment tribunal by Roger Maskell, a former official at the union, who admitted his involvement in the malpractice but now believes he was made a scapegoat and is claiming unfair dismissal. He says the general secretary reneged on a deal to compensate him for loss of office.
Mr Maskell's statement alleges that Sir Ken, once known as the Prime Minister's favourite union leader, was fully aware of both the voting irregularities and an attempt to cover them up. The papers state that apart from double-voting, at least four white- collar branches of the union nominated Sir Ken without holding a meeting.
The Amicus-AEEU leader, who will receive a pay-off of at least £300,000 when he hands over to his left-wing rival on 1 January, has denied any knowledge of malpractice.
The Maskell statement, written by his lawyer, says: "The applicant's view is that his dismissal was for political reasons so as to deflect the allegations on to himself as a relatively senior officer of the union and away from the general secretary, and to satisfy 'No 10' on the run-up to the dispatch of ballot papers."
The tribunal submission by Mr Maskell suggests that the union had an authoritarian leadership that tried to use threats and intimidation to retain its power. The former union official alleges that Sir Ken urged on his supporters by declaring: "There are no no-go areas. Deliver the nominations or face the consequences." The general secretary is alleged to have told his lieutenants that those not fully supporting his re-election would be "severely dealt with".
It has since been established that computer records were amended to switch officials from one branch to another. In some cases the officers involved voted in their original branch and in the one to which they were transferred.
In his statement Mr Maskell said he spoke to Sir Ken on the phone after the exposure of the double-voting and the general secretary had expressed concern that Mr Simpson might give the press information.
The statement added that Sir Ken was "particularly worried" that Mr Simpson's sources in the union would be able to recover computer-based evidence of officials switching branches.
A spokesperson for the union said last night: "The charges that Maskell has made will be hotly defended. We are sure the tribunal will reach the correct decision."
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