Within two hours of his ringing endorsement of the Union at the Scottish Tory party conference in Glasgow, Mr Major's political fightback was thrown into disarray when Mr Rifkind told Channel 4 News: "I have no problems about the principle of devolution or constitutional change if there are proposals which can apply throughout the UK and create a stable constitutional structure."
Mr Rifkind, a former Scottish secretary, emphasised the proviso that "what is absurd and foolish about the Labour party's proposals is to create what is in effect a federal solution for Scotland, Wales and Northern Ireland and no change for England."
But the intervention, which some Tories suggested was a sacking offence, came in stark contrast to Mr Major's earlier warning that a devolved Scottish parliament would be a "stepping stone" towards an independent Scotland.
The Prime Minister won a five-minute standing ovation after ending his speech with a passionate appeal for Scots Tories to become "shock troops in the battle to preserve the Union".
But Mr Major appeared to acknowledge majority support for a Scottish parliament: "I know some people are very proud, most people, understandably, immensely proud, of their Scottishness and they would like to see a Scottish parliament.
"I understand that feeling but we have to look at the risk of what that would bring with it - the dangers of that being a stepping stone towards an independent Scotland."
Effectively throwing open the topic for fresh debate within the party, Mr Rifkind said that if Labour could make up its mind on a structure that was meaningful throughout the UK "then I could see some logic in it".
Mr Major has long since made his opposition to devolution a key weapon in fighting Labour; the issue was a significant feature of his 1992 general election campaign and is planned to figure prominently in the next one.
The marked difference in approach threatened to undermine a carefully prepared strategy by the Prime Minister to revitalise his Government's fortunes with a wide-ranging initiative to consult party members and an attack on Labour's devolution plans.
The blow to the Government's credibility on the question comes as Mr Major faces the uphill struggle in the Perth and Kinross by-election in less than a fortnight.
Earlier he had responded to mounting criticism that his government was out of touch with "middle England" by giving a pledge to listen to his party's demands for a change in policies.
The Prime Minister's promise to listen signalled the anxiety in the Conservative Party leadership to staunch the haemorrhage of its support, but it was ridiculed by Jack Straw, the Shadow Home Secretary, who said if Mr Major did listen he would abandon privatisation of British Rail and the nuclear power industry.
Mr Major's attempt to reunite his party came as Tony Blair pledged a "new understanding" with business based on a "new approach" from his party, and promised that industry would be fully consulted on the introduction of a minimum wage and the Social Chapter.
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