Alliance Boots is being bought by private equity

Carlyle head Robert Easton said it made investments for the long term as KKR head Dominic Murphy said the idea its aim was to asset strip was "ludicrous".

Also present were 3i and Permira who echoed this, saying they had helped create jobs in firms they bought.

But the industry chiefs were struck dumb when asked how much tax they paid.

Wednesday's hearing was the first time that the industry's leaders had had to defend their position to UK politicians in such a public hearing.

We do a tremendously good job with workers and stakeholders but the industry has not done a good enough job with our employees Robert Easton, Managing director, Carlyle Q&A: Private equity

Private equity has been criticised for paying just 10% tax on gains made on companies they invest in, for using too much debt to finance deals as well as for cutting jobs.

The bosses were called in front of the Treasury committee to be grilled over several issues, including their low rate of tax, the opaque environment in which they operate and that they cause job losses while enriching themselves.

Time frame

Union leaders have been calling for the sector to be more tightly regulated, saying it is the workers who have been losing out when private equity firms make acquisitions.

Recent years have been a golden age of British wealth creation Robert Peston, BBC business editor Read Robert's blog in full

"We do a tremendously good job with workers and stakeholders," said Mr Easton.

But he added that "as an industry we have not done a good enough job with our employees" and should do more.

Union worries

Jack Dromey, deputy general secretary of the Transport and General Workers Union section of Unite, said: "Workers' rights are the missing link in the current debate on private equity."

We've produced world class returns for [our pension funds]. And in an era where pension fund deficits are a big issue Damon Buffini, managing partner, Permira

He added that "the measures designed to protect pay, terms and conditions when work transfers from one company to another, needed to be extended to cover private equity deals."

Certain cases have become emblematic for unions of what it sees as the negative side of the industry - such as the acquisition by Permira of AA.

After AA was bought in 2004, about one third of its workforce of 10,000 lost their jobs.

Pensions

Private equity funds have increasingly hit the headlines in recent years, snapping up a growing number of UK companies, such as pharmacy group Alliance Boots.

When KKR boss Dominic Murphy was asked how long his firm KKR would keep Boots, he said it anticipated owning Boots "for at least five years" and that he wanted all employees to be satisfied with its pension fund.

Permira head Damon Buffini argued that private equity deals were to the benefit of millions of pensioners.

"We have 30 million pensioners in our pension funds. And we've produced world class returns for them in an era where pension fund deficits are a big issue. And I think that's a big positive for the country."

Transparency

Last week, Peter Linthwaite, the head of the British Private Equity and Venture Capital Association, which represents the UK's private equity industry, unexpectedly resigned after he was widely criticised for a weak showing before the committee.

The Treasury select committee is looking at four main areas regarding tax levels in the industry:

• treatment of debt and equity
• carried interest
• stamp duty and the role of taxation
• the competitiveness of the UK's tax regime