But the same firms have gone to extraordinary lengths to avoid scrutiny of the tax arrangements of their Irish operations. So convoluted are they that they seem to have confused their own lobby group.

An international tax expert has said that the government needs to resist pressure from US multinationals to prevent Ireland becoming a fully-fledged tax haven, such as Jersey or the Cayman Islands. A list of such tax havens is being targeted by a law proposed last month in the newly Democrat-controlled US Senate. If Ireland were to be labelled a 'tax haven' in Washington it could prove disastrous to Ireland's reputation, say observers.

Richard Murphy, director of UKbased consultancy Tax Research, said that there was growing unease internationally about the way multinationals exploited Irish corporate law to avoid disclosing their financial activities.

Intel Ireland, for example, whose general manager Jim O'Hara warned last week that the Irish government should no longer suggest that the current corporate tax rate of 12.5 per cent was "as good as it gets", is registered in the Cayman Islands, where companies do not publish any financial information.

Microsoft, following a November 2005 expose in the Wall Street Journal about its use of Ireland as a "low-tax haven" to shield it from paying US taxes, reregistered its controversial Irish subsidiaries, Round Island One and Flat Island Co, as unlimited companies last year, which means they no longer file public accounts.

Microsoft Ireland managing director Joe Macri, in a January speech to the Leinster Society of Chartered Accountants, warned that Ireland's favourable tax rate was the only reason foreign multinationals were based in Ireland.

It has also emerged that the American Chamber of Commerce in Ireland (AmCham) has been overstating the amount of corporate tax paid by US firms each year in Ireland. A spokeswoman claimed that the figure of Euro2.7bn contained in its recent National Development Plan submission was incorrect. The chamber had used the figure since 2005.

She said that the correct figure for 2006 was Euro2.4bn while the 2005 figure was Euro2.1bn - Euro600m less than previously stated.

"The key relationship between these companies and Ireland is tax. They are now trying to break that relationship by not disclosing their accounts and trying to get the government to reduce their tax rate, " said Murphy.

Murphy said that there was a risk that Ireland could be listed in a new US Senate bill backed by presidential hopeful Barack Obama. The bill aims to penalise companies that use named tax havens.

However, the head of international business and development at Trinity College, Frank Barry, said that the presence of US multinationals was "completely benefical" for Ireland and that there was no prospect of a clampdown by the US tax authorities.

"It's actually beneficial for them because firms are liable in the US for the difference between the Irish tax rate and the US one. So they get a greater share of what's left."

Barry said that tax wasn't the only reason why multinationals chose to locate here. "We have such a long history and experience of dealing with multinationals that the whole economy is perfectly structured to capture foreign investment."

A spokesman for the Department of Finance emphatically insisted that Ireland wasn't a tax haven. He said it was ironic that some commentators were using freely available information from Ireland's tax system to brand it as one.

"The low rate of corporate tax is necessary to attract inward investment that would otherwise go elsewhere or would not occur at all, " he said.

Meanwhile, Intel Ireland said it was as a leader in good corporate governance. "To the extent that we are legally required to report, we report, " said a spokeswoman.

She said the firm was based in the Caymans because it "allowed the most flexibility with respect to cashflows generated by Intel's global operations".

AmCham said that its members' corporate structures were their own business.