PARTISAN Tory attempts to cripple Labour’s finances by cutting off union funding could be defeated in the Lords after being criticised yesterday by the Prime Minister’s own ethics adviser.

Lord Bew, the chairman of the committee on standards in public life, said the plan, which is part of the Trade Union Bill, is “not in the spirit” of the committee’s advice.

Moving to an opt-in system for trade union political levy payers, whereby members would have to state in writing that they want to make a donation to Labour, was recommended by the committee in 2011.

But it was part of a broad package of changes advocated which also included a £10,000 annual donation cap that would have hit Tory coffers.

The report stated that “the temptation to implement some parts while rejecting others would upset the balance we have sought to achieve.”

And in a statement published after the second reading of the Bill in the Lords, Mr Bew said: “I insist on this as a central point.

“To extract one element which deals with trade union funding without implementing the other reforms is not in the spirit of the 2011 report.

“Nobody who reads it can be in any possible doubt about that.”

It was the second blow to the Tory Bill in two days after the Equality and Human Rights Commission said that it did not comply with international labour laws.

The influential peer’s damning verdict on the move, which Labour believes will dent its finances by £6 million a year, could see it scuppered in the House of Lords.

Labour is hoping to unite with Lib Dem and cross-benchers to defeat the funding fix when the Bill reaches the committee stage next month.

TUC general secretary Frances O’Grady said the Lords debate had “exposed once again how ill-thought-through and partisan the government’s Trade Union Bill is.

“Widespread concerns were raised across the House about the threat this Bill poses to good industrial relations and fair treatment at work,” she said.

“It is essential that ministers listen before lasting damage is done.”