Two polls carried out last week reveal that support for the Tories has slumped from 40 per cent of the vote at the last general election to about 15 per cent today. The Scottish nationalists, runners-up in 1992, are in the lead with about 40 per cent and Labour has jumped into second place with more than 20 per cent.
Although almost one-third of voters remain undecided, the poll findings have forced John Godfrey, the embattled Conservative candidate, on to the defensive. Campaigning in Perth yesterday, he insisted that the Tories had "won every argument" in the by-election but could not be confident of victory. Privately, party activists are resigned to losing the seat, held by the late Sir Nicholas Fairbairn, by up to 7,000 votes.
Despite its strong showings in the polls and bold predictions by Tony Blair that after local election successes in middle England Labour can win in "middle Scotland", Labour, too, is downplaying expectations. Officials fear that after the party's recent victories south of the border, defeat by the Scottish National Party will be seen as a severe setback in Scotland.
Douglas Alexander, the Labour candidate, yesterday declined to predict a Labour win. He dismissed support for the nationalists as votes "for convenience, not conviction" and insisted that "the only way to make John Major sit up" was to vote Labour.
The SNP, however, was not so coy. Roseanna Cunningham, the party's candidate, said the SNP would take the seat. She accused Labour of abandoning commitments to the welfare state and turning its back on the "traditional Scottish values of common decency". The nationalists alone now represented "mainstream Scotland", she said.
Following the Scottish Conservatives' conference in Glasgow last week, when leading Tories questioned John Major's policy on the Union, the campaign has been dominated by the constitutional question. Yesterday, Mr Godfrey, who has been telling voters on the doorsteps that he is the "Unionist and Conservative" candidate, described the contest as "the constitutional by-election".
He launched a fresh attack on SNP "separatism", saying that an independent Scotland would have a budget deficit of some £8bn. Labour's plans for a tax-raising Scottish parliament threatened inward investment, he added. A vote for the Tories was a vote for Scotland, "for the Union and for the monarchy as we know it".
Miss Cunningham dismissed Mr Godfrey's calculations as "clumsy and infantile". The Government's own figures showed that an independent Scotland would have a budget surplus of £30m, she insisted. And Jack McConnell, the general secretary of the Scottish Labour Party, said the Tories' arguments were irrelevant. "This by-election is not about the status quo, it is about change," he said.
For the Liberal Democrats - registering about 5 per cent in the polls - Veronica Linklater said that federalism, with devolution in England and Wales as well as Scotland, offered the only solution to Britain's constitutional problems.
She dismissed Mr Godfrey's comments as "irrelevant to the overwhelming majority of Scots. Conservative policies belong in the dustbin," she said.
Voters go to the polls next Thursday.
nGeneral Election 1992: Sir Nicholas Fairbairn (Con) 20,195; Roseanna Cunningham (SNP) 18,101; Merv Rolfe (Lab) 6,267; Malcolm Black (LibDem) 5,714. Conservative majority: 2,094.