Scottish Conservatives will join their party colleagues south of the Border in hailing the result as a foretaste of victory at the next UK general election.

But if a Tory triumph in the Cheshire seat previously held by Labour veteran Gwyneth Dunwoody takes Mr Cameron a step nearer Downing Street, could it also be preparing the way for Scotland to set off down the road to independence?

The SNP would seize on the return of an English-dominated Conservative government at Westminster as another good reason why Scotland should take charge of all its own affairs.

There are elements in the Conservative Party down south who would be happy to see Scotland leave the UK, not least because it would increase the chances of prolonged Tory rule in England.

However, it is still premature for the Tories to assume the keys to No 10 are about to fall into their hands.

They may have been riding high in all the opinion polls for the past few weeks, on the back of Labour's badly-judged abolition of the 10p tax band and concerns about the economy.

However, it is almost certainly two years until the next general election and political fortunes can change quickly.

Just a few months ago, Gordon Brown was basking in strong approval ratings and there were mutterings that David Cameron might have to be replaced as Tory leader.

Even now, while he has a large lead in the opinion polls, focus groups are reporting that people compare Mr Cameron to an estate agent and think there is "something not quite right about him".

Despite the headlines after the English and Welsh local elections earlier this month, Labour's poor showing did not translate into a Tory tide sweeping across the country.

In the north of England, the Conservatives won control in Bury, but they could not get a single councillor elected in the big cities of Manchester, Liverpool, Newcastle or Sheffield.

In Reading, where Labour were said to have lost their last bastion in the south, the party is now back running the council as a minority administration.

In Scotland, the party is revelling in the new-found influence which it can wield thanks to the minority status of the SNP Government. But the Tories continue to languish in the opinion polls for the Scottish Parliament.

Although party officials say recent UK-wide polls suggest the Conservatives will do well here in the next Westminster election, they start from the low base of just one Scottish MP.

A party insider says: "We are not going to gain more than three or four seats at the most – and that would be seen as a really good result."

Fifty years ago, Tory support in Scotland was strong. Indeed, the Tories are the only party ever to have won more than half the votes at a general election – they took 50.1 per cent in 1955.

BUT all that has changed. If Mr Cameron were to become Prime Minister on the basis of big swings in the south, but still with only patchy support in the north of England and hardly any representation in Scotland, he could find himself presiding over an extremely polarised country.

The SNP would almost certainly try to brand his government as an English regime out of touch and out of sympathy with Scotland.

Mr Cameron's Tories would be painted as the English party, just as they were under Margaret Thatcher.

A senior party source says: "It would look bad because the make-up of the government would be south-east England-based.

"I'm sure David Cameron would try to have a mature relationship with Alex Salmond and he would try to work together. But the SNP is desperate for a Tory government because it's much easier to fight against a London-centred Tory government than a Labour government with a Scottish Prime Minister and a lot of Scottish MPs."

Tory bosses are delighted with the election of former Scottish Office minister George Kynoch as the new deputy chairman, defeating veteran right-winger Bill Walker.

A senior source says: "Bill is seen as a figure of the past who doesn't really fit in with the Conservative revival. He is an unreconstructed Thatcherite who doesn't like the Scottish Parliament."

Whether it signals a "modernisation" of the views of the grassroots is another matter.

There has been some discontent inside the Tory Party over its involvement in the cross-party Calman Commission looking at more powers for the Scottish Parliament. Critics feel it was a mistake to get too close to Labour, especially in view of Wendy Alexander's previous troubles and latest referendum debacle.

An insider says: "Some members are quite rightly annoyed. All Wendy's contortions made us and the Liberal Democrats look really stupid. We signed up to the Calman commission and suddenly she announced she was backing an early referendum.

"There is definitely unease about whether we should be part of it." But the critics are expected to keep quiet – for now at least.

The result from Crewe and Nantwich is not expected until around 2.30am. If the Tories triumph it would be their first by-election win from Labour since Ilford North in 1978. Ironically, expectations are now so high that anything less than a massive victory risks being seen as a setback.

But if they do win, no-one wants to spoil the party.