Conservative leadership candidate Mr Kenneth Clarke yesterday angrily denounced Baroness Thatcher's intervention in the campaign, claiming she was out of touch and had alienated young voters.
With Mr Clarke expected to reveal former prime minister and Lady Thatcher's successor, Mr John Major, as his next big-hitting supporter, possibly later today, the Conservative leadership race looks set to become increasingly bitter and personal.
Lady Thatcher entered the leadership fray, declaring her support for Mr Iain Duncan Smith, in a letter to yesterday's Daily Telegraph in which she claimed Mr Clarke would lead the Conservative Party to "disaster".
The former pro-European chancellor was one of Lady Thatcher's Cabinet colleagues who, in 1991, walked into her Downing Street office and told her she no longer had their support, forcing her to step down as prime minister.
In her letter endorsing the right-wing Mr Duncan Smith, Lady Thatcher used the strongest language to condemn Mr Clarke.
"I simply do not understand how Ken could lead today's Conservative Party to anything other than disaster," she said, pointing out that his pro-European views were at odds with those of the majority of the party.
"Time and again the Conservatives would be exposed as either hopelessly split or deeply cynical, either openly rebelling against their leader or going along with policies which they knew, and which others knew, to be wrong," she added.
Lady Thatcher also criticised Mr Clarke for failing to take his share of the blame for the Tory election defeat in 1997. "It would have been reassuring to hear from Ken Clarke about some of the mistakes which in 1997 led the Conservative Party to the greatest defeat in its history." And referring to criticism of Mr Duncan Smith's lack of ministerial experience, she added: "After all he, not Iain Duncan Smith, was one of those who made [those mistakes]."
Baroness Thatcher's intervention is likely to influence mainly right-wing Tory members considering where to put their cross on leadership ballot papers. But Mr Clarke insisted Lady Thatcher's comments would do little to encourage new voters to join the Conservatives.
He accused her of trying to "hijack" the Tory Party conference every year regardless of who was party leader and said she had conspired with Eurosceptics to destroy Mr Major's term in office.
"When she appears in the election it is usually no longer, I'm afraid, our finest moment. Of course she's a very keen Conservative, but as she's got older she's got ever more fixed views. Margaret has made the choice more stark than it need be," Mr Clarke said.
The support of former prime ministers is important for rank and file Conservatives, but has little impact otherwise. Lady Thatcher was angered by reports earlier in the campaign that she would endorse Mr Michael Portillo and her backing of Mr Duncan Smith is hardly surprising.