A contender to be the next general secretary of Unite has sparked a huge row with the trade union’s most senior Scottish official over the notorious Falkirk débâcle in 2013.

Gerard Coyne, considered the main challenger to Len McCluskey, said Unite’s role in the infamous Labour candidate selection row, and the subsequent industrial dispute at the Grangemouth petrochemical plant, had a “retrograde” impact on members’ terms and conditions. He also said it was a “classic” case of “messing around” in local politics.

Returning fire, Unite’s senior Scottish official Pat Rafferty launched a withering attack on the leadership candidate, accusing him of trying to “trash” the union and preferring the company of sections of the “hostile media” to his own union members.

Unite is in the middle of a three-way contest to determine who will be the next general secretary after McCluskey triggered an election by standing down. The race is also being seen as a proxy battle for the future of Labour, as McCluskey, who is standing again, is a staunch supporter of Jeremy Corbyn while Coyne is a moderate.

The leadership battle has been characterised by personal attacks, with Coyne claiming McCluskey spends too much time on “Westminster power games” and McCluskey accusing his rival of peddling “smears”.

Speaking exclusively to the Sunday Herald, Coyne spoke about two of the key controversies of his rival’s period in office. In 2013, this newspaper revealed how Unite had recruited a large number of members to Labour in a bid to help McCluskey ally Karie Murphy get selected as the party’s Westminster candidate in Falkirk.

The Herald: Gerard Coyne is challenging for the Unite leadership

Picture: Coyne

The political row snowballed into a huge industrial dispute amid claims union reps at the Ineos petrochemical plant at Grangemouth had used company time for political activity.

“Falkirk was a classic illustration of the union messing around in local politics and it having a negative impact on industrial policy,” said Coyne. “It could not be a clearer example of why we should not be messing around in those arenas. Falkirk was the touchstone for the changes in the Labour party rules around the election of the leader and all we’ve ended up with in relation to the changes in the Labour party,” he added.

On nuclear weapons, Unite delegates helped pass a motion at the 2015 Scottish Labour conference that opposed the renewal of Trident, even though the union represents workers in the sector. After the vote, the industrial shop stewards committee at Babcock Marine Clyde – the company that operates the Faslane nuclear base – said that members felt they were being treated like “mugs” by Unite.

Coyne said: “I can understand how they would feel disappointed by their union, particularly as the policy position has been that Unite would only see the end of the commitment to Trident if there was a clear alternative… And the truth is that isn’t going to happen.”

Rafferty responded stingingly about Coyne: “Astonishingly, his latest journey across the border has seen him trash the union he seeks to lead. He added: “And he is wrong again about Unite’s defence members. I know because I led the push at Scottish Labour for the party policy to mirror that which was developed with, and backed by, Unite’s defence members which quite clearly says that Unite’s priority is protecting defence members’ jobs and communities.

“Lastly, Falkirk. As Gerard Coyne also well knows, this union did nothing wrong. We were taking forward the party’s own policy – to encourage working men and women to join the party their forefathers built, to re-engage so the party again reflected their aspirations,” he said.

Gail Cartmail, Unite’s acting general secretary, said the blame for the Ineos dispute lay solely with the employer and added that the union protected defence jobs.

A spokesperson for McCluskey’s campaign said the candidate had been nominated by both the Faslane and Coulport branches.