The “dire situation” was revealed during a misconduct hearing into the union’s election result, where it was revealed that more than 158,000 members left between June 2011 and January 2013 after refusing to pay their membership fees for six months.
Mr McCluskey, 64, won the election in April 2013 with 60,000 more votes than his opponent, Jerry Hicks, an unemployed former Unite shop steward. Mr Hicks complained to the Certification Officer, the trade union watchdog, to ask how 158,000 "former trade union members" had been allowed to vote in the election.
Mr Hicks told a misconduct hearing in London yesterday that Mr McCluskey and Unite's executive council knew about the lapsed members when it called the election three years before it was scheduled in 2015. He said they were sent ballots with a letter telling them about union benefits and that they could pay their arrears to stay in the union.
Mr Hicks said: "I think people could have construed that they weren't eligible to vote or had to join the union to vote. But they shouldn't have been sent a ballot at all, they should have been excluded or made to rejoin."
Turnout for the election was 15.2 per cent of the 1.3 million ballots sent to union members. Only 3 per cent of the 158,000 lapsed members voted.
Mr Hicks said Mr McCluskey and Unite's executive council called the election early to avoid the "embarrassment" for Labour of it coinciding with the general election, and to avoid real opposition to his re-election. He said: "It was brought forward by three years — an amazing amount of time. It had all the hallmarks of an election race not expected to happen."
Mr Hicks told the hearing that the election was the dirtiest he had ever been involved in.
Steve Turner, Mr McCluskey's "campaign manager", is now being investigated by Unite after retweeting a claim that Mr Hicks "condoned sex crimes against women".
Mr Hicks said: "1 was a 1,000-1 outsider, an unemployed man from Bristol against the general secretary, but it was clear we were doing far better than they had ever imagined."
Michael Ford, representing Unite, said the union did not recognise that the 158,000 workers who had refused to pay their fees for six months were not still members of Unite.
David Cockburn, the Certification Officer, said he would make a decision on the application to annul the election result within four weeks.
If the election is annulled, Mr McCluskey will remain in his post because his five-year term of office will still be in effect from the 2010 election.
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