ALEX Salmond last night accused the Unionist parties of taking a "kamikaze" approach to the independence debate, warning that their refusal to share the pound would backfire with voters.

As the No camp continued to attack the First Minister for failing to identify a Plan B on the currency, Salmond came out fighting against what he called Westminster's "bullying diktat".

The issue has electrified the referendum since Tuesday's TV debate between Salmond and Alistair Darling, when the First Minister was booed for refusing to say what he would do if, as they have promised, the Unionist parties vetoed a currency union with an independent Scotland.

A Survation poll published yesterday found a four-point jump in support for No, to 57% among decided voters, following the debate.

It also found 69% of people wanted Salmond to publish his Plan B on the currency.

Salmond insists that Labour, the Tories and LibDems are bluffing, and would agree to sharing the pound after a Yes result because it would make economic sense for Scotland and the rest of the UK.

Writing in today's Sunday Herald, he claims the No campaign have an obsession with a Plan B, despite the Scottish Government's expert panel of economists, which includes two Nobel laureates, concluding last year that a currency union was the best option for both nations.

"As such, the No campaign's tactic of saying no to a currency union makes absolutely no economic sense," Salmond writes.

"But it also makes no political sense, and is a tactic that is a deeply dangerous one for them.

"They are playing with fire, and they risk neglecting a cardinal rule of political campaigning - namely, not learning your lesson from past mistakes."

He said that when the Conservative Chancellor George Osborne ruled out a currency union on a visit to Edinburgh in February, "the Scottish electorate decided to stand up to the bullying diktat from Westminster, and support for independence shot forward in the polls.

"The No campaign think that spending the rest of this campaign telling ordinary people in Scotland that they have zero entitlement to a currency that is already theirs and which they can't be stopped from using in any case, they will pay a heavy price."

The First Minister repeated his veiled threat to walk away from Scotland's £120 billion share of the UK national debt if there was no currency union, a move which would saddle the rest of the UK (rUK) with £5bn more in annual debt interest payments.

That was a prospect Unionist parties would struggle to sell to voters, he said.

"It's for reasons like these that Westminster's pronouncements on the pound are more kamikaze than convincing. It is Scotland's pound and we are keeping it come what may," he said.

However, the anti-independence parties showed no sign of relenting over the issue yesterday.

Darling, chairman of Better Together, said he would continue

to harry Salmond over a Plan B when the pair met in BBC TV debate on August 25.

The three Scottish No party leaders accused Salmond of sending voters a deeply misleading leaflet promoting independence which said "we'll keep the pound" despite the veto warning.

"We therefore invite you to take the chance to set the record straight about your Plan B. Unless you answer this question, it will follow you up to polling day - because people have a right to know the truth," the three said.

The No camp also seized on the Survation poll which showed an eight-point swing to No in the two days after the TV debate.

The survey of 1010 people found 50% support for the Union, 37% for a Yes and 13% undecided.

Stripping out don't knows, support for Yes was 43%, down three points since a Survation poll published on Sunday, while support for a No was 57%, up four points since Sunday.

The survey found the adjectives most frequently applied to Salmond were weak (18%), uninformed (13%) and dishonest (11%), while those applied to Darling were knowledgeable (21%), strong (16%), nervous (11%) and honest (11%).

Blair MacDougall, Better Together's campaign director, said: "The reason Alex Salmond lost the debate with Alistair Darling wasn't just about style, it was about substance.

"Mr Salmond cannot answer the most basic question about independence: what money would our wages, pensions and benefits be paid in?"

SNP Treasury spokesman Stewart Hosie pointed out the same Survation poll found 40% thought the No parties would agree to a currency union, compared to 39% who thought the opposite.

He said: "Despite a new onslaught of scaremongering from the No camp parties, it is clear that people in Scotland still aren't buying Westminster's currency bluff."

Scottish Labour leader Johann Lamont will today claim a Yes vote would produce "a new wave of austerity" for Scottish families.

Speaking in Glasgow, she will quote Neil Kinnock's famous warning to voters when Mrs Thatcher was Prime Minister in the 1980s.

"I warn you not to be ordinary. I warn you not to be young. I warn you not to fall ill. I warn you not get old," she will say.

"Salmond may rave against austerity, but he knows a new, additional wave would come after independence ... That means cuts to our NHS, our schools, our pensions and our social security.

"This can be avoided with a No vote."

A spokesman for Salmond said: "It was Gordon Brown who warned the No campaign about bullying Scotland on currency - it is our pound too, and an independent Scotland will keep the pound."

On Thursday, Salmond said his expert panel named four alternatives to sharing the pound.

The first, using the euro, Salmond ruled out.

Two others, a new currency with a free-floating exchange rate and a new currency pegged to the pound, he described as "perfectly viable but not as good as keeping sterling".

The First Minister also raised the possibility of Scotland using the pound regardless in an informal union, so-called sterlingisation, in the same way Panama has adopted the US dollar.

However, Scottish banks would no longer have access to the Bank of England as a lender of last resort in a crisis in this arrangement.

Economists last week warned sterlingisation would see Scottish banks fleeing south to enjoy greater financial protection in the rUK.

Sterlingisation has also been discounted by Salmond's own economic experts as "not likely to be a long-term solution".

With just five weeks to polling, Salmond has no alternative but to stick with his Plan A.