Internet search engine giant Google has moved to shield from public view the affairs of its holding company in Ireland, which has annual royalty income of more than €300 million.

The California-based group applied to the Companies Office this week to re-register Google Ireland Holdings Ltd as a company with unlimited liability. While such a move is not without risk, unlimited companies have no obligation to file their annual accounts publicly.

The reasons for Google's decision are unclear, but the move comes amid deepening scrutiny by the tax authorities in the US of the mechanisms used by US multinationals to reduce their exposure to tax in their home market.

Google is among many US groups in Ireland that take advantage of the 12.5 per cent corporate tax rate and other incentives here to reduce their tax bill in the US. It is increasing its Irish staff to 1,000 from 300 but says the bulk of this employment is not tax-driven.

In official filings with US regulators last year, the group said that it had "significantly lowered" its tax bill for the first three quarters of 2005 thanks to its Irish operation. The effective tax rate dropped to 31 per cent from 39 per cent during 2005, it said.

Google is not the first US group to re-register a big Irish subsidiary as unlimited. Following press coverage in the US, Microsoft took steps last March to re-register as unlimited two of its Irish units, Round Island One and Flat Island Company.

The Irish legal adviser to both Google and Microsoft is the Dublin firm of solicitors, Matheson Ormsby Prentice, which has an office in California.

Google's Dublin office said yesterday that no-one was available to respond to queries about the move to change the legal status of Google Ireland Holdings.

There was no response from the press office in Google's US headquarters.

The most recent accounts for Google Ireland Holdings show that it took in royalty income of $388.55 million (€307.21 million) last year and had a loss before tax of $46.66 million. The company owns some of Google's intellectual property and is part of a structure that saves its parent millions of dollars in tax.

Companies Office records indicate that the status of Google's other Irish company, Google Ireland Ltd, is unchanged. That company had a turnover of $603.27 million in 2004 and made a pretax profit of $5.25 million in that year.