But the committees will not hear from the Tory deputy chairman himself after he failed to respond to an invitation to give evidence in what one Labour member described as a "terrible discourtesy".

The House of Commons Public Administration Select Committee will hold a one-off hearing into the issue of propriety and peerages, sparked by Lord Ashcroft's announcement earlier this month that he has "non-domiciled" status for tax purposes.

And peers on the Sub-Committee on Lords' Interests will consider a Labour MP's complaint that Lord Ashcroft breached the code of conduct of the Upper House by failing to fulfil a pledge to become a permanent UK resident as a condition of his ennoblement.

The hearings come amid reports that a Panorama investigation into Lord Ashcroft has been shelved by the BBC following threats of legal action, and may not be screened until after the general election.

The revelation of Lord Ashcroft's non-dom status has been highly embarrassing to the Conservatives as the billionaire businessman gave former leader William Hague a written assurance in 2000 that he would take up permanent residence in the UK.

His pledge came after he was twice turned down for a peerage, in part because of concerns that his residence in the central American state of Belize made him a tax exile.

The Public Administration Committee will hear evidence from Baroness Dean of Thornton-le-Fylde, a member of the Lords vetting panel which finally approved his nomination after receiving his promise to live in the UK.

And it will hear from former Whitehall mandarin Sir Hayden Phillips, who oversaw an agreement that later amended Lord Ashcroft's assurance so he would become a "long-term" rather than "permanent" UK resident, clearing the way for him to claim non-dom status. Mr Hague did not learn about the change until a few months ago, and current Conservative leader David Cameron was not told until even later.

The change allowed Lord Ashcroft to pay UK tax only on British income, not on the bulk of his earnings which come from overseas. Liberal Democrats have estimated the arrangement has saved him more than £120 million over the past decade.