Lord Ashcroft's return to the Tory fold is a marriage of convenience

Lord Ashcroft is the biggest single donor in Conservative Party history, and is credited with putting them in power in 2010 (Getty Images)

When Conservative fortunes hit rock bottom in 1997, the party had good reason to be grateful to Michael Ashcroft. The tycoon, who had made his fortune abroad, pumped £10m into the party’s depleted funds.

William Hague repaid his generosity by nominating him for a peerage, causing controversy because the newly ennobled Lord Ashcroft did not appear to be a UK taxpayer. Despite that long-running problem, relations with David Cameron started well, but had turned sour by the time the general election was over.

Since he turned his back on Conservative headquarters in December 2010, Ashcroft’s money and energies have been channelled into political publishing and commissioning informative opinion polls. Last year, it emerged that he is working on what is expected to be an unfriendly biography of the Prime Minister.

If Lord Ashcroft has started putting money into the Conservative Party again, it will not be because he has become a Cameron fan, but because his polls are telling him next year’s election might let Ed Miliband into Downing Street. For Lord Ashcroft, that prospect is even worse than another Cameron-led administration.