Leaders of the the controversial private equity industry yesterday tried to rescue their battered image, claiming that they were a "force for good" in the British economy.

Appearing before the Commons Treasury Committee, four of the main players in the industry sought to dispel their reputation as corporate "asset strippers", claiming that they were good for jobs and good for profits.

It was in sharp contrast to the picture painted earlier to the committee by trade union leaders who likened the secrecy with which the industry operated to the Mafia.

The private equity operators also struggled to convince the MPs, who, in a series of testy exchanges, accused them of "opaqueness" and colluding over their evidence to to committee.

Labour MP George Mudie even claimed that they had even brought in public relations consultants to provide "coaching" on how to answer questions at the evidence session.

Dominic Murphy of Kohlberg Kravis Roberts and Co - which recently took over the high street chemists Boots - delivered increased employment, increased investment and increased growth.

He dismissed suggestions that the industry simply took advantage of low interest rates to buy firms in highly "leveraged" deals, only to slash the workforce and sell off the assets, before selling them on at a vast profit.

"I think the caricature is inaccurate," he said. "Private equity is a force for good."

Damon Buffini of Pemira said that private equity firms were delivering "world class" returns for the pension funds which invested in them at a time when pension fund deficits were a major issue.

He said that businesses acquired by Pemira "engage in the social fabric" - with one firm in Nottingham donating 2,000 hours of employ-ees time to a "right to read" programme and recycling 10,000 tonnes of used bingo tickets.

Robert Easton, the managing director of the Carlyle Group, added: "My experience of private equity has only been positive."

However, MPs on the committee were incredulous when none could say how much their companies paid in capital gains tax.

Committee chairman John McFall said: "You guys are the really bright guys. You are the masters of the universe. I ask you how much you pay in capital gains tax and you can't tell me? I find that amazing."

Mr Murphy however denied that they were the beneficiaries of a "loophole" in the capital gains tax regime originally designed to encourage new, start-up companies.

"There are no tax loopholes," he said. However, Philip Yea, the chief executive of 3i, warned against any changes to the tax rules - which recently led one private equity operator to boast that he paid tax at lower rate than his cleaner - which would penalise the industry.

"I think there is a risk that this activity, which is increasingly global, could move elsewhere," he said. Despite claims by the witnesses that they were committed to transparency, there was increasing frustration among MPs at the answers they were receiving.

"There is an opaqueness about this. We are struggling for information," Mr McFall said.

Earlier, however, Jack Dromey, deputy general secretary of the Unite union, complained that unions had frequently struggled to find out who owned actually owned companies after they were taken over by private equity firms.

"The public knows more about the Cosa Nostra than private equity," he told the committee.