Alex Salmond has given his clearest indication yet that he would want an independent Scotland to keep the pound, even without a formal currency pact, after stating "we are keeping it, come what may".

The first minister insisted, in an article for the Sunday Herald, that "there is literally nothing anyone can do to stop an independent Scotland using sterling, which is an international tradeable currency".

Writing five days after a bruising encounter with Alistair Darling in STV's live debate on independence, Salmond insisted that the UK parties were bluffing when they repeatedly ruled out a currency pact after independence.

Salmond argued there was clear economic and political logic for a formal agreement to share sterling and the Bank of England, as he tried to persuade voters in Scotland that he was correct to keep fighting for a deal. It would avoid UK businesses paying extra transaction costs to trade in Scotland, mean Scotland would pay its share of the national debt and allow UK politicians to honour the democratic will of Scottish voters who had backed independence, he wrote.

Despite stating he would not admit defeat, Salmond clearly hinted he was still leaving the option open of using sterling without a deal.

Repeatedly saying Scotland could use sterling regardless of any deal, he concluded that it was "Scotland's pound. And we are keeping it, come what may."

Salmond's fightback came after the first full opinion poll following his faltering performance on STV suggested the yes vote had been damaged. It found a four point rise in no votes to 50%, and four point fall in yes votes to 37%.

The Daily Mail poll by Survation, which has frequently given among the highest yes votes of any pollster, found that 69% of voters wanted Salmond to draw up an alternative currency plan. However, 40% of voters also agreed with Salmond that the UK veto on a currency union was a bluff, against 39% who said it was not.

Defiantly accusing his opponents of issuing a "bullying diktat" against Scotland, he said that Ed Miliband's pledge on Friday that he would veto a deal to share sterling in next year's Labour election manifesto was a "hasty gambit" that would backfire.

Salmond said the clear economic and political case for a sterling zone were underlined by Miliband's admission on Friday, in an interview with STV, that UK businesses might face "hundreds of millions of pounds" in extra transaction costs if Scotland had a different currency.