THE Conservative Party’s biggest donor faced accusations of a lack of patriotism last night, after confirming on his website that he is non-domiciled for tax purposes.

The billionaire businessman, who has given millions of pounds to bankroll Tory campaigning in marginal seats, admitted he does not pay tax in the UK on earnings overseas.

But he insisted his arrangements were in line with assurances he gave when granted his peerage a decade ago that he would take up permanent residence in the UK.

But Justice Secretary Jack Straw said Lord Ashcroft’s surprise announcement – after years of speculation – meant he had failed to keep his promise.

He accused senior Conservatives of "concealing the truth" for 10 years.

Mr Straw said David Cameron was trying to use Lord Ashcroft’s money to "buy the election" while Liberal Democrat leader Nick Clegg said it was "wholly wrong" for a non-dom to fund a campaign.

Lord Ashcroft has been central – both by providing financial backing and in his role as Tory deputy chairman – to the policy of targeting marginal seats which if successful could see Mr Cameron in Downing Street.

He has made donations worth more than £4m through Bearwood Corporate Services since Mr Cameron became leader in 2005.