The Electoral Commission was last night urged to investigate claims that millionaire Tory donor Lord Ashcroft had channelled money to the Conservative Party from overseas.

The Electoral Commission was last night urged to investigate claims that millionaire Tory donor Lord Ashcroft had channelled money to the Conservative Party from overseas.

A newspaper article suggested some of his donations had been sourced from a company in Belize.

While there is no suggestion that he has broken the law, Labour said the claims raised fresh questions about his support for the Tories.

Political parties are only allowed to take donations from companies that are registered in Britain and "carrying on" business.

Lord Ashcroft has donated millions of pounds to the Tories in recent years through a company called Bearwood Corporate Services (BCS), which is UK-registered.

According to a newspaper, however, BCS is the beneficiary of cash which has moved through a series of deals from a Belize-based company called Stargate Holdings.

The peer, a deputy chairman of the Conservative Party, has attracted controversy for some time over his failure to say whether he is resident and pays tax in the UK.

Labour chief whip Geoff Hoon MP said: "This latest investigation raises serious questions about whether the ban on overseas donations is being circumvented.

"Is Lord Ashcroft's Bearwood Corporate Services generating all the revenue it uses in the UK to fund the Tories? Or are foreign profits being channelled to the Tories?

"For months David Cameron has failed to answer key questions on Lord Ashcroft. He has failed to make clear whether he is on the electoral register in the UK and if he is how long he has been so."

Labour MP John Mann yesterday wrote to the Electoral Commission's chief executive, Peter Wardle, asking him to investigate the matter.

A Conservative Party spokesman said: "The Conservative Party compliance unit applies strict tests to all company donations in accordance with guidance.

"The donations from Bearwood Corporate Services were legal and permissible."