Labour big-hitter Tom Watson has reopened the trade union selection row, accusing the party of creating a "huge injustice" in Falkirk.
The influential former campaigns co-ordinator said two members suspended over the episode had suffered 'trial by spin doctor' and urged Labour chiefs to publish the full inquiry into what had happened.
Pundits say his comments, in a Guardian interview, will pile pressure onto Ed Miliband.
Watson said suspended candidate Karie Murphy, who was his office manager, had done nothing wrong.
And he slated Labour's decision to refer the case to the police.
“I thought it was silly to report the allegations to the police, bordering on wasting police time," he said.
Miliband attempted to reform Labour's relations with the unions in the aftermath of the Falkirk scandal, in which it was claimed Unite had tried to fix the selection of the seat's general election candidate by packing the constituency with 100 or more of its own members, some of them without their knowledge.
Watson, who resigned with an elaborate letter to Ed Miliband, told The Guardian Unite had not recruited any members without their knowledge, describing the furore as a "storm in a teacup".
On the party's refusal to publish the report, he said: "I feel that the two suspended members, who have over 50 years of voluntary service to Labour between them, deserve a fair hearing rather than trial by spin doctor."
He also accused anti-union Labour figures, including Peter Mandelson, of exploiting the row, and called for unions' role within the party to be increased, rather than weakened.
And he claimed the complaints against Murphy had come from a rival candidate.
Labour dismissed his criticisms of the Falkirk investigation, The Guardian said.
It comes as Ed Miliband is accused of not making himself heard against a resurgent Tory party.
But Watson backed the leader, saying: "There might be reasons why the Labour party's not getting its message across, but it's not Ed."