Steve Richards: Watch Scotland... the surge of nationalism could transform politics south of the border

Traditional party loyalties are breaking down in unpredictable ways. Formerly self-assured experts have given up placing bets on the outcome of council by-elections in England. Labour can do unexpectedly well in the South-east of England. The Tories can score a hit in the North. The only surprise is when there is no surprise.

There are no patterns anymore. The national media waits with sweaty excitement for the clash between Brown and Cameron. In swaths of the country the attention is on other battles, between Labour and the Liberal Democrats in the north and Conservatives and the Liberal Democrats in parts of the south. The only depressingly common theme is that smaller parties such as the BNP perform fairly well in the current anti-politics mood. Some voters make their dangerous protests by endorsing the extreme right.

In Scotland the disillusioned have an alternative vehicle. Once more the SNP rides high in the polls. More dramatically a recent poll suggests that around 51 per cent of Scottish voters support independence. Cabinet ministers and Labour MPs are alarmed, wondering fearfully whether the SNP will emerge as the largest party in the elections for the Scottish parliament next May, a sensational outcome that would make the current storms reshaping the English political landscape seem pathetically tame.

It is not difficult to see why the SNP appeals well beyond the party's core vote. The Liberal Democrats are part of the coalition with Labour in Edinburgh. They are in no position to benefit from protest votes. The Conservatives' partial recovery in England is not replicated in Scotland. They are nowhere to be seen. The SNP is best placed to benefit from a reaction against the Labour Government in Westminster, the Lib/Lab coalition in Edinburgh and the failure of the Conservatives to make headway. It stands to do so in a way that feeds dramatically into the febrile state of politics in England.

Of course there is cause for caution when contemplating apocalyptic scenarios. Support for Scottish nationalism oscillates wildly. For years the SNP has risen in ways that threaten to be overwhelming and then the roar has subsided, the equivalent of a surfers' wave that fails to deliver. Even so there is not much that is likely to happen between now and the election in May to repel the current wave.

In particular the SNP performs well when revenues from North Sea oil are high. Currently the Treasury gets nearly £12bn from North Sea oil. In 1993 it was closer to £1bn. The old slogan about Scotland's oil is much more powerful when the fuel soars in value by billions of pounds.

The SNP is also agile in its appeal. While positioned on most issues to the left of Labour it is winning over Tories who have given up waiting for their party to recover. In next month's issue of Prospect the Conservative-supporting historian Michael Fry writes forcefully about why he is switching to the SNP. Fry argues that Scotland's dependence on a generous English subsidy has led to a bloated public sector and an unproductive economy. Without an effective Conservative Party he regards independence as the only solution: "The Scots' Tories, nine years on, neither uphold their old policies nor seek new ones - they prefer to have no policies at all."

The rise of the SNP does not mean that independence will follow. Indeed Fry's argument about the huge gap between taxes raised in Scotland and the high level of public spending would probably terrify most voters into opposing independence if a referendum is held. But the rise of the SNP and the mere possibility of a referendum will fuel debates in England about its relationship with Scotland.

Some senior Conservatives, including members of the Shadow Cabinet, have raised already the possibility of English MPs alone deciding on legislation that impacts on England rather than the rest of the UK. The Mayor of London, Ken Livingstone, has asked in the past why the capital should contribute generously to Scotland while it struggles to fund a decent public transport system. The author of the funding formula in which Scotland is the main beneficiary, Lord Barnett, has called for a revision of the rules. What would happen to these debates if Scotland stuck two fingers up at the rest of the UK by making the SNP the biggest party in its parliament?

None of the debates are straightforward. The Conservatives' leadership makes it clear that the support for separate votes on English legislation is not a firm commitment. London is about to benefit from generous dollops of public funding, probably much more generous than first predicted, as it prepares to host the Olympics. More generally there is as yet little tangible anger in England at the dominance of Scots in the media and politics. The historian, Niall Ferguson, ubiquitous and Scottish, has expressed amazement at the acceptance of the Scottish dominance in England, wondering whether any other country in Europe would be quite so tolerant.

Yet the prospect of a dramatic SNP breakthrough is enough in itself to cause political eruptions. Recently I asked an anxious cabinet minister why he was so bothered about the precise timing of Mr Blair's departure. He had been arguing that Mr Blair should go soon rather than wait until the summer. His reply was stark: "The break-up of the United Kingdom is at stake." The minister suggested that under a new leader it was possible that Labour in Scotland would do better, at least holding back the SNP wave. The SNP benefits from an anti-Blair mood as well as a backlash against an administration that has ruled in Edinburgh since 1999.

At a more parochial level tensions are rising between Scotland's First Minister, Jack McDonnell, and the government in London. Most recently Mr McDonnell has demanded that the Scottish Parliament be given the same powers to slash levels of corporation tax that might be ceded to the Northern Ireland Assembly. Gordon Brown is resisting such a move, arguing that the demand is a gift to the SNP with its implication that Scotland should function almost as an independent economy. Mr McDonnell argues that only by making such concessions can Labour stave off the threat posed by the SNP. Nearly every move in Scotland is viewed through the possible ascendancy of the SNP.

The prospect of an SNP triumph is causing tensions on every front from the date of Mr Blair's departure to spending policies in Scotland and England. At its most dramatic Mr Brown could become a Scottish Prime Minister at a moment when the SNP wins in Scotland. In such circumstances his carefully planned first hundred days would be dominated by a constitutional crisis that called into question his right to be a Prime Minister over the UK. Watch Scotland. The outcome of May's election, and the more immediate fears over what the outcome might be, will have an impact on us all.

s.richards@independent.co.uk