Britain's senior tax official has warned companies that have moved their corporate residence out of the UK for tax purposes that years of scrutiny by HM Revenue and Customs (HMRC) may lie ahead as the tax authority seeks to establish whether they really have made a "clean" break from the country.

Speaking to the Financial Times, Dave Hartnett, the permanent secretary for tax at HMRC, expressed scepticism that companies which have switched their corporate residence to another jurisdiction could truly claim to have severed their ties with the UK to the extent that they are no longer taxable there.

Hartnett suggested that while board meetings may be taking place in other countries, there is evidence to suggest that key company decisions are still being made from the UK in some instances, and he said that "investigation and litigation in the UK" will establish whether a company has truly redomiciled.

Since last year, there has been a steady stream of companies which have publicly announced plans to relocate for tax purposes, including pharmaceutical firm Shire, publishing company United Business Media, advertising agency WPP, Brit Insurance, engineering firm Charter, and investment company Henderson. Ireland, Luxembourg and Switzerland are among the main beneficiary countries of these corporate defections.

While the UK's corporation tax rate, at 28%, isn't the highest, many company executives and business leaders have spoken out recently to condemn the government's record on corporation tax policy. The much-anticipated foreign profits tax reforms have been generally welcomed, but the government's accompanying anti-avoidance (debt cap) provisions have been harshly criticized, as have other smaller but regular changes to tax legislation which have led to increasing uncertainty in the UK tax system.

In August, Bart Brecht, chief executive of Reckitt Benckiser, told the Daily Mail that his company was considering a move from the UK because "clearly the tax situation in the UK is not improving for companies.?