The BBC tonight cancelled a Panorama documentary on the business and tax affairs of Lord Ashcroft, just hours before it was scheduled for broadcast last night. Click here to read more

Lord Ashcroft, the outgoing deputy chairman of the Conservative Party, continued to avoid millions of pounds in UK tax, despite his pledge to become a full British taxpayer, according to a wide-ranging investigation into his financial and business affairs to be aired by the BBC tonight.

A Panorama programme on the billionaire Tory donor was originally scheduled to air before the General Election, when Lord Ashcroft was in charge of the party’s campaign in marginal constituencies, but the corporation delayed broadcast amidst wrangling with Lord Ashcroft's lawyers, and extended the programme's scope.

The investigation spans three countries where the peer has controversial interests, including the Caribbean tax havens of Belize and the Turks and Caicos Islands, as well as the UK. His lawyers told the BBC before broadcast: "Our client has denied any impropriety or wrongdoing in respect of any of the matters that you have raised."

Lord Ashcroft’s opaque tax affairs have proved a thorn in the side of David Cameron’s Conservative party, and the Panorama broadcast will ensure that the issue does not fade quietly as the peer formally steps down from the deputy chairmanship at a party meeting today.

The programme claims that Lord Ashcroft transferred ownership of one of his main companies on the eve of a new law that forces members of the House of Lords to pay tax on all their worldwide income. On 5 April, the peer moved his 25 million shares in Impellam Group into a trust for the benefit of his children. On 6 April, new legislation came into force that would have cost him an estimated £3.4m in inheritance tax.

“The billionaire businessman hasn’t broken any rules by using the family trust, but his actions appear to conflict with the coalition government’s stance on tax avoidance,” the BBC said in a press release for the programme, which airs on BBC1 at 8.30pm today.

The Independent revealed in March that plans to broadcast the investigation before the election had provoked furious protests from Conservative headquarters. Senior Tories fired off letters of protest to the director-general of the BBC, Mark Thompson, and the chairman of the BBC Trust, Sir Michael Lyons. In the end, the decision to delay broadcast was taken because Lord Ashcroft’s lawyers disputed key parts of the programme and to give the team of journalists more time to unravel his network of offshore companies.

The peer is taking legal action against The Independent over two reports on his business interests in the Turks and Caicos Islands last November.

Panorama says that British detectives working on a corruption inquiry in the TCI are looking at loans provided by Lord Ashcroft’s bank to two local politicians. The investigation started after a Commission of Inquiry headed by retired Judge Sir Robin Auld found a high probability of systemic corruption in the islands and requested a criminal investigation of five government ministers. The British government suspended the TCI constitution last year and the islands are being run from the UK Foreign Office, which is now led by Lord Ashcroft’s political ally William Hague, who nominated him for a peerage when he was the Conservative leader in 1999.

The peerage was eventually granted in 2000 after Mr Ashcroft gave Mr Hague a written promise that he would become a UK resident. For the next nine years, he refused to answer questions about whether he was a UK taxpayer, until his hand was forced two months before the General Election this year, when he admitted he was not fully resident in the UK for tax purposes and so paid no tax on his huge overseas assets.