Alex Salmond
Alex SalmondReuters

Downing Street has insisted the Treasury's move to guarantee all UK debt in the run-up to the Scottish independence vote was a simple case of ensuring market stability - but Alex Salmond was quick to claim it was a "common sense decision" and a victory for his campaign.

Salmond could not hide his delight after the Treasury confirmed it would take responsibility for all the UK's £1.4 trillion debt, come what may. And, privately, it was being suggested he believed he now had "the whip hand" over the issue and, crucially, his promise to keep the pound as Scotland's currency in the event of a "yes" vote.

He said he was ready to shoulder Scotland's fair share of the debt, but repeated his view that it would only be part of negotiations which saw the pound remaining as the nation's currency, something ministers have suggested may not be possible.

"Today's announcement makes clear that Scotland would be in an extremely strong negotiating position to secure that fair deal," he said.

Chief Secretary to the Treasury, Danny Alexander, said the move had been prompted by investors raising concerns over the debt, which in turn raised the prospect of increased interest rates.

"An independent Scotland would have to pay that money back to the UK government," he said. Officials have not revealed what they believe that share might be.

Perhaps more significantly, Downing Street sources struggled to say what levers there were to ensure an independent Scotland would actually pay back any cash, suggesting a refusal would undermine the country's international financial credibility.

Leader of the "no" campaign Alistair Darling, however, claimed the nationalist leader was "playing with fire with his irresponsible threats to default on Scotland's debts if he doesn't get his way on currency.

"It appears that the First Minister needs a basic lesson in economics. The UK Pound is a monetary system underwritten entirely by the UK Government. It's not an asset to be shared like the CD collection after a divorce."

It is certainly the case that the markets might not warm to the government of an independent Scotland if it refused to repay its debt and Salmond must be careful not to undermine his own position with investors.

But, in the short term, he appears to have won a major boost to his pledge to keep the pound.