The Conservative leadership plot thickened last night as Mr Michael Ancram quit as party chairman and declared himself the fourth candidate in the race to succeed Mr William Hague.
Mr Ancram - grandee son of the 12th Marquess of Lothian and married to Jane, youngest daughter of the Duke of Norfolk - presented himself as a "unity" candidate.
An apparently reluctant runner, he declared: "I am putting my name forward because I have been convinced by so many people . . . that I cannot stand aside."
However, Mr Ancram was immediately identified as a "stop Portillo" candidate. In a pointed swipe at Mr Portillo, the former Northern Ireland minister urged his party not to turn its back on the last four years.
"I am not standing to fulfil long-held personal ambition but to offer the Conservative Party the chance to choose the path of unity, to grasp the opportunity for reflection rather than hasty action, to renew our appeal to the people without tearing up our roots," he said.
Mr Ancram's decision to enter the race complicated predictions about its final outcome. If he survives the parliamentary party's "primary" election and makes second place on the ballot he might expect, as a former party chairman, to attract considerable grass-roots support.
The bookmakers William Hill immediately cut Mr Ancram's odds from 50-1 to 9-1, although one punter had already placed a £500 bet at the more generous price. Mr Portillo remains the odds-on favourite at 4-9, with Mr Iain Duncan Smith at 3-1. However all the odds will change next week if the former Tory chancellor, Mr Kenneth Clarke, declares his candidacy.
Mr Portillo's aides claim he has the support of up to 100 of the 166 Conservative MPs.
Even if Mr Clarke proved the choice of the constituencies, he has publicly questioned whether he - a passionate advocate of early British membership of the euro - could actually lead such a Eurosceptical party.
The depth of opposition to Mr Portillo on the traditional right was underlined yesterday by Lord Cranborne, who said the shadow chancellor had shown himself to be indecisive.
Recalling the 1995 episode when Portillo supporters established a campaign headquarters while he publicly dithered on whether to oppose Mr John Major, Lord Cranborne said: "He found it an extremely agonising decision to take. I thought it was a plain, straightforward one. I don't think you should show that you're agonising in public."