BRUISED Better Together leader Alistair Darling is to ramp up his attack on the SNP's currency plans as he tries to pick himself up after his television debate defeat against Alex Salmond.

The former Chancellor will be joined by former Prime Minister Gordon Brown at a campaign rally in Dundee today, where they are expected to issue a stark warning that interest rates would soar if - as the First Minister stressed during Monday night's clash - an independent Scotland refused to pay its share of UK national debt.

The two, whose relationship soured towards the end of Mr Brown's time as premier, will be sharing a platform for the first time since 2010, as the No campaign launches a final push for votes.

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Mr Darling, who visited a factory in Renfrewshire yesterday said the campaign was a "fight right down to the wire", and will continue to put the currency question at the heart of the No campaign despite his warnings falling flat with television viewers.

Mr Salmond yesterday credited his victory at Kelvingrove Art Gallery and Museum in Glasgow to his promise to negotiate only for his Plan A, a formal currency union between Scotland and the rest of the UK, if Scots vote Yes.

Better Together strategists remained upbeat despite Mr Salmond's widely acknowledged victory in the programme, which was watched by 843,000 people in Scotland and 4.8 million across the UK on the BBC and Sky.

A snap Guardian newspaper/ICM poll of just over 500 viewers found 71 per cent judged the First Minister the winner, with 29 per cent backing Mr Darling.

The 200-strong audience's vocal support for the First Minister, and occasional heckling of Mr Darling, prompted an informal complaint yesterday to the BBC from Better Together. Despite that, No campaign insiders privately admitted Mr Salmond came out on top.

However, they claimed his bullish performance may have done little to woo undecided voters.

During the debate the First Minister again declined to set out his preferred alternative to sharing the pound and the Bank of England in a formal currency union with the UK, a proposal ruled out by the main UK parties.

Instead he said he had "three Plan Bs". His favourite appeared to be "sterlingisation", under which an ­independent Scotland would continue to use the pound informally with no access to the Bank of England. In that scenario, said Mr Salmond, the country would not shoulder its share of the UK's £1.4 trillion debt.

Danny Alexander, Chief Secretary to the Treasury, condemned the threat, warning it would add to Government borrowing costs and increase interest rates for homeowners and consumers.

He said: "Everyone in Scotland knows if you don't pay back a debt, it ruins your credit history for years to come. Such a threat will not just send a shiver through the financial markets, it is a menace to every single family in Scotland."

The snap poll suggested Mr Salmond was the more appealing personality and had the better arguments. He was also the overwhelming winner among women voters, who are less likely than men to support independence, say polls.

However, the sample of 505 people did not change their minds on how to vote next month as a result of the clash.

Before the debate, 44 per cent backed Yes, 46 per cent No and 10 per cent were undecided. Afterwards, support for Yes and No rose a percentage point to 45 per cent and 47 per cent respectively, as the don't knows dropped to eight per cent.

In a move to calm the markets, the Treasury confirmed earlier this year it will continue to honour the UK's debts if Scotland becomes independent, although it stressed the new state would be expected to pay a "fair" share.

Mr Salmond has argued the prospect of the country walking away from annual debt repayments of £5 billion would force the UK to agree a currency union.

Yesterday he insisted he had "argued persuasively" on currency and Mr Darling had "muffed it". He said: "The No campaign had their chance, their bluff has been called. People have, I think, overwhelmingly in Scotland now in poll after poll, shown that we want to keep the pound. We're fighting a campaign to get a mandate from the Scottish people on common sense for a common currency.

"That's what won the debate last night and that's the message that's going to resonate over the next three weeks."

Meanwhile, it has been revealed David Cameron, due in Scotland this week, did not watch the live TV debate but relied on later news reports about it.

Yes Scotland suggested the Prime Minister was "perhaps ... distancing himself from the faltering No campaign" while a source close to the First Minister, noted: "He may not have been paying attention but the London Establishment is now starting to wake up to the fact this referendum campaign is going right down to the wire and it is the Yes campaign that has all the momentum."