Former employment lawyer Carr was appointed by the government to investigate the conduct of unions following an incident in Grangemouth. In November 2013, Unite members were accused of attempting to intimidate managers in a dispute at a chemical plant.
The initial purpose of the investigation was to suggest changes to the law that would prevent unions from acting unlawfully or unethically during industrial disputes. In March, TUC general secretary Frances O’Grady described the probe as a "headline grabbing party-political stunt".
In a statement released on the Carr Review's website, the QC said he didn't feel capable of delivering an "evidence-based judgement" without it being construed as a political action.
"I have become increasingly concerned about the quantity and breadth of evidence that the review has been able to obtain, from both employers and trade unions, relevant to its terms of reference," he said.
"In addition, I am also concerned about the ability of the review to operate in a progressively politicised environment in the run up to the general election."
Carr said he had agreed with secretary for business, innovation and skills Vince Cable and cabinet office member Francis Maude that while a report will still be filed in the autumn, no legal recommendations will be included.
The news comes after Maude, in an unrelated statement, called for tighter rules around unions polling their members on industrial action last month.
Unite general-secretary Len McCluskey accused the government of "shooting itself in the foot" and sabotaging the very review it had commissioned.
"In their haste to attack trade unions, they have embarrassed their own appointee, Bruce Carr, into accepting this report for what it was all along – a desperate pre-election stunt to smear democratic trade unions and their members," he said.
