In November 2013 David Cameron asked Bruce Carr QC to lead a review of industrial relations in Britain.
The Prime Minister was angered by some of the protests the Unite union carried out during a particularly bitter industrial dispute at the Grangemouth plant in Scotland.
Bruce Carr was asked to examine whether the law needed changing to prevent "harassment" and "intimidation".
In August 2014 Mr Carr abandoned his review claiming the "politicised environment" had made his job impossible.
Since then the government has drafted the Trade Union Bill, which is now at select committee stage in the House of Lords.
The Business Secretary Sajid Javid says the bill is designed to stop what he called the "endless" threats of strike action and to make the balloting process more democratic and accountable.
Tonight, in an exclusive interview with ITV News, Mr Carr has warned that the bill shifts the balance of power "too much in favour of the employers" and has urged the government to make changes.
Mr Carr's comments are particularly devastating for the government given that he acted for both unions and employers over the years, indeed his wealth of experience of industrial dispute was precisely the reason he was approached to conduct the review in the first place.
His views will delight the unions and will probably also surprise them.
At the time they dismissed him a a "Tory stooge" and refused to cooperate with his review.
Mr Carr's complaint is that the Trade Union Bill in its current form will do more harm than good.
He believes that plans to raise the ballot threshold, limit the period in which strike action can be taken and restrict trade union funding, combined with the possibility that employers will be allowed to bring in agency workers to replace striking workers, will force unions outside the law.
"Unions will resort to tactics which sit outside the traditional framework of ballots...and they will feel themselves driven into more of a guerrilla warfare situation," Mr Carr said.
He has urged the government to make changes to what he described as "an unhelpful piece of legislation."
A report by the Mirror earlier this week suggests ministers are considering change.
One remedy Mr Carr suggests is to allow unions to conduct online ballots.
Until now the government has insisted such ballots are not secure enough, although that's precisely the method the Conservative Party used to select Zac Goldsmith as their candidate for London Mayor.