Where will 'winding up' Westminster lead?

Pink champagne in hand, Alex Salmond has been enjoying himself recently, doing what seems to come naturally; winding up Westminster.

Why does the Scottish National Party and its former leader matter? Because, if the general election polls are right, in six weeks time the SNP could hold the balance of power in the House of Commons.

If neither Labour nor the Conservatives win a majority, one of them would need votes from smaller parties to govern - and the pollsters suggest the SNP could be the biggest of those smaller parties, perhaps with about 50 MPs.

This week Mr Salmond, who hopes to be among that number, launched a thousand newspaper columns written by observers apparently astonished and horrified at his statements of the obvious.

Shock! SNP MPs would not vote for a Tory Queen's Speech, said Mr Salmond. Did anyone think they would?

Horror! They would try to influence a Labour chancellor's budget. Did anyone think they wouldn't?

Mr Salmond's appearance on the Andrew Marr show was described by Conservative defence minister Anna Soubry as "one of the scariest" she had heard for a very long time.

"The audacity is astonishing," she told the man himself as they cosied up on the studio sofa, adding waspishly: "There was a wonderful debate in Scotland. You lost it."

Ms Soubry was echoing sentiments which have abounded for weeks now.

Reheating the most incendiary phrase in British politics Allan Massie in the Mail on Sunday foresaw the River Thames foaming with blood.

"The English bulldog has woken from a long sleep, and is beginning to snarl," he warned.

For Max Hastings, in the Daily Mail: "A historic tragedy beckons for the UK... the backlash in the south will prove bitter indeed."

So who benefits from all this?

As it happens, the rhetoric might suit both the SNP and the Tories, at least in the short-term, in their battles against a mutual enemy: Labour.

North of the border the SNP are trying to portray themselves as the party that stands up for Scotland and its interests against the pitiless Tories.

To the south, the Tories want to present themselves as the defenders of England and its interests against the socialist hordes, kilted or otherwise.

This clash of two nationalisms is disheartening for the significant chunk of Scotland which viewed last year's debate about independence as distracting and divisive rather than energising and exciting.

In particular it's bad news for the Scottish Conservative leader Ruth Davidson who took to the pages of the London Evening Standard to say so.

"The SNP is not Scotland and Scotland is not the SNP," she warned, describing nationalist tactics as "cheap, dirty politics" designed to "stoke division" and "annoy the rest of the country into pushing Scotland towards the exit".

Unfortunately for her, Tory strategists in London appear to have chosen to throw fuel on to the fire, taking the opportunity to paint the Labour leader Ed Miliband as weak and the SNP as power-crazed.

Mr Salmond, said a Tory party spokesman, was plotting to "sabotage the democratic will of the British people in order to make Ed Miliband prime minister".

Robin McAlpine, director of the Common Weal think tank, part of the wider independence movement but not affiliated to the SNP, says such outrage is absurd.

He says: "If England as a nation wants to be an electoral unit of their own then they have to have a campaign of independence. If England wants to be independent of Britain, then start leafleting, start marching, and have your campaign."

The Scottish Labour leader Jim Murphy is scathing about the approach of both his rivals.

"Alex Salmond loves the sound of his own voice," he says. "It's only surprising the Tories are giving him a megaphone to amplify that voice."

"The fact is that the Tories can't win in Scotland so they need someone else to defeat the Labour Party for them."

Mr Murphy insists voters north of the border will see through this attempt to "divide and rule".

For her part, the leader of the SNP, Scotland's First Minister Nicola Sturgeon, denies that she has sent Mr Salmond southwards to stir up dissent. Nor, she says, is he doing so off his own bat.

"That is not the objective of the SNP in this election," she insists.

"We're not there to prod anybody or get a rise out of anybody.

"We're there to seek to stand up for Scotland to get better policies coming out of the House of Commons."

To satisfy its burgeoning membership - now said to be above 100,000 - the SNP will need those policies to be radical, says Mr McAlpine.

Otherwise "they're going to shed those members," he says.

This move to the left has "already started," Mr McAlpine argues, with an economic document from the Scottish government giving "greater economic equality the same weight as economic growth".

It is "a big step," he says.

Mr McAlpine also defends Mr Salmond against the charge of provoking the English.

"I don't think he's driving a wedge between Scotland and England," he says.

"He's driving a wedge between the politics Scotland believes in, a progressive social-democratic politics, and a politics that he doesn't believe in, the vicious anti-immigrant, anti-welfare politics which seems to be quite strong in the south of England."

Whether that is the case, and whatever the motivations of both the SNP and the Conservatives, there are big risks ahead.

If the Tories get it wrong they could put the union they support in peril. The SNP faces the opposite problem. In particular, three potential scenarios could be tricky for the party:

None of these options looks particularly attractive for the nationalists, especially when you consider that the SNP is still tainted in the eyes of some Scots for voting 36 years ago today against the Labour Prime Minister Jim Callaghan in a confidence motion.

Mr Callaghan lost by one vote and the era of Margaret Thatcher followed, to the horror of many people in Scotland.

Now, Alex Salmond and Nicola Sturgeon clearly think they could cause a lot of mischief before a crunch point like this was reached, amending bills here and there and squeezing out concessions.

In the meantime Ms Sturgeon's message can be summed up as: you wanted us to stay in the union, so now we want to have a say in it.

The trouble is everybody knows that staying in the union is not the SNP's principal aim.

Why would stable and secure governance of the United Kingdom be a priority for a party which doesn't believe the UK should even exist?

Any politician thinking of quaffing champagne at this stage cannot know whether they will end up raising a toast or weeping into their glass.