Jack Dromey, the deputy general secretary of the T&G section of Unite, said that self-regulation of the private equity industry was "worse than useless".

Speaking in a TUC debate on private equity in Brighton this morning, Mr Dromey said that there was a pressing need for the government to act to defend workers when private equity companies entered the equation.

In a passionate address, the deputy union leader, whose wife is Labour's deputy leader, Harriet Harman, said: "Private equity makes the Cosa Nostra look like a model of openness and transparency by comparison.

"They take our members' jobs, they pile our companies with debt, they fleece all of us by not paying their fair share of tax and then expect us to be grateful.

"All the evidence we have seen is that jobs, pay, terms and conditions and pensions are put at risk when these companies come in," he continued.

Earlier this year, the unions mounted a campaign to pressure the government to close down loopholes and improve the accountability and transparency of private equity firms.

Unions accuse these companies of borrowing large sums of money to buy up and asset-strip companies, then "slashing" jobs and hard-won conditions of employment for workers.

TUC delegates today backed moves to establish a database to track the activities of private equity funds both in the UK and overseas.

Unions also want consultation rights for staff where companies are taken over by private equity, and a review of the impact of pensions regarding the transparency of information provided by the industry.

Mr Dromey added: "We recognise that sometimes they will be the only show in town. That is why the shroud of secrecy must be lifted, the tax regimes altered to make them fair, but above all our members must be offered protection."

Earlier this morning, Richard Lambert, the director general of the Confederation of British Industry, faced tough questions from delegates over the tax arrangements of private equity firms following his keynote address to conference.

Mr Lambert said that private equity companies found themselves playing a "different role" in the economy after enjoying a period of huge growth.

But he acknowledged that the private equity industry should disclose more information than it had done in the past.

"There are other stakeholders who need to know what is going on," he said.