Fire up the Quattro – and let's see who rises from the Ashes

This decade, the job has fallen to the convention-defying Europe minister, Chris Bryant, who became the first gay MP to be married in the Commons just last weekend. After spending his honeymoon in Edinburgh, Mr Bryant felt moved to write a letter – only in the archaic worlds of politics or religion could writing a letter still make headlines – pointing out that independent Scots would need passports to visit England and would find Euro entry denied because of Scotland's whopping share of UK debt.

Presumably, that debt isn't bigger than Iceland's – still managing to negotiate EU entry despite shameful inclusion on the UK's terrorism register. And if it is, Labour has just revealed a rather bigger problem for the whole of the UK – no Euro escape route for us, should the UK's triple "A" credit rating finally fail.

As for passports to cross borders… come on. The Irish don't require them, and the English – encircled by Schengen states with open internal borders – might just as easily end centuries of splendid Isolation and join the human race. This half-hearted scaremongering will patronise Scots who bother to think about it and rile core Nationalist voters. But scaremongering – like phone-selling – must work sometimes. And talk of debt, borders, passports and post-independence hassle may be just enough to coax deserters from the 2007 Holyrood elections back Labour's way.

All is fair in love, war and elections – so they say. Except this weekend another reality has been at work. As you sow, so shall you reap.

After coshing the SNP, Labour scored a spectacular own goal down south with a poster depicting David Cameron as Ashes to Ashes cop Gene Hunt.

The slogan says, "Don't let him take Britain back to the 1980s", and Labour clearly hoped it would associate the Tory leader with Thatcher in the Eighties. Instead, it associated the supposedly toffee-nosed, out-of-touch, old Etonian with the coolest detective on TV.

So delighted are the Tories with this Easter gaffe, they've reproduced the mocked-up picture of Cameron astride an Audi Quattro, with a new slogan, "Fire up the Quattro. It's time for a change."

No matter that actor Philip Glenister insists he hates what Margaret Thatcher did to Britain. The two posters will alternate on the same digital billboards in London and Manchester, after both parties double-booked the same sites.

You couldn't make it up.

And the Liberal Democrats couldn't have a better backdrop for their own guerrilla marketing campaign – thus far conducted on affordable YouTube – the Labservatives.

"Scandal, recession, war," says a Gordon Brown figure that morphs into David Cameron, Margaret Thatcher, Jim Callaghan, John Major and Tony Blair, "There's no substitute for experience."

"We've had 65 years to get it right," runs the slogan on another billboard. "So what's another five?"

With Labour and the Tories using the very same election poster, the Lib Dems have to believe voters will finally see the truth of their oft-repeated message that Labour and the Conservatives are two faces of the same battered coin, trying vainly to sound distinctive.

If they can't ram the point home now, will they ever manage?

Perhaps the two parties are so evenly matched that the cleverest cartoonists will win the day?

Perhaps voters are so stunned and scared that the nastiest negative campaigners will sway them?

Or the British public might just be getting ready for substantial change.

While Tony Blair was grabbing the limelight last week, a shift in public opinion was taking place. Vince Cable's spot in the chancellors TV debate prompted a 4 per cent surge in support for the Lib Dems, taking support equally from Labour and the Tories, according to ICM. A weekend poll suggests the Tories may have mopped up those losses.

But if the much- maligned and overlooked third force in UK politics has been able to flex its electoral muscle – against all the predictions of world-weary hacks, pundits and big business donors – the televised chancellors debate may have been a turning point. And if a bit of fresh-faced, cheeky questioning from a minor party leader can reap such dividends in opinion polls, the SNP and Plaid Cymru have new evidence with which to argue against their exclusion from the BBC's "top table".

The received wisdom has been that the televised debates will be boring and unwatchable. Admittedly, without Vince Cable the odds of hearing more "Mr Bean" quality jibes aren't great. But the Lib Dem leader's job isn't hard. All Nick Clegg has to do is explain the voyage of rejuvenation Britain must undertake to crack open the class-ridden, over-centralised, undemocratic shell that's stifled growth and protected the Big Two Parties from genuine challenge since the Second World War.

And if he makes his case well, he might just change the course of this election… and of history.

Many Scots will find this possibility unbelievable.

We are used to the Lib Dems coming last and reform being considered impossible south of the Border. We are used to hearing English politicians and commentators cling to archaic but familiar bits of governance. We know already that a "hung" parliament on 6 May will not be described as "balanced", that no reference will be made to Welsh and Scottish "minority" experience and that young men from discredited banks will tell voters, instead, that "indecision" will destroy confidence in the UK.

Most of us think we can write the script from here and bet that the inexplicably threatening prospects of coalition, negotiation or conciliation after 6 May will cause English voters to stick to the devils they know.

It is just possible they won't.

As the country waits for Gordon Brown to make his move, it's still all there to play for.