ALEX Salmond has downplayed the question of what currency an independent Scotland would use, saying that in another referendum the “key battleground” would be trade.

The former First Minister also said Nicola Sturgeon would present a “range of currency options” if she called another referendum, and suggested autumn 2018 as a likely date.

Labour said the idea of debating trade under independence, without knowing which currency trade would be conducted in, was “Alex in wonderland” thinking.

Currency is seen as a key weakness of the Yes campaign in 2014.

At the time, Mr Salmond insisted an independent Scotland would keep the pound in a currency union with the rest of the UK, despite then Tory chancellor George Osborne ruling it out.

The other pro-independence parties, the Scottish Greens and Scottish Socialists, both wanted a new Scottish currency, but bit their tongues to maintain the appearance of Yes unity.

There is now an active debate in the SNP about a future currency position, with MPs Tommy Sheppard and George Kerevan advocating a separate Scottish currency.

Speaking on BBC Sunday Politics Scotland, Mr Salmond referred to Ms Sturgeon’s proposal to keep Scotland in the EU single market, while the rest of the UK left in a hard Brexit.

He said: “What that does, of course, is suggest that the key battleground in terms of economics in any future independence referendum is not going to be, as it was the last time, the currency, but is going to be trade and access to trade and access to markets. Because that is what the UK Government is jeopardising and that is what an independent Scotland could secure.”

Asked if a future Yes campaign would stop arguing Scotland could keep the pound regardless of UK government resistance, Mr Salmond said: “Nicola Sturgeon knows her own mind.

“She’ll be able to outline the range of currency options that are open to Scotland.

“But the key argument that I see coming in this referendum, if that’s what happens, in terms of economics, is going to be what secures Scotland’s trade, our access to markets, on which prosperity depends. I think independence has a winning argument on that framework and I expect to see it expertly deployed by Nicola Sturgeon.”

Ms Sturgeon last year established an SNP Growth Commission under corporate lobbyist Andrew Wilson to update the case for independence, including on currency.

A new currency could give Scotland maximum economic freedom, but could also be costly, complex, time-consuming and potentially unpopular with the public.

A recent BMG poll for Labour found only 21 per cent of Scots in favour, compared to 68 per cent wanting to keep the pound.

Scottish Greens co-convener Patrick Harvie has also said a transition to independence based on a new currency could take 10 years, not the 18 months the SNP outlined in 2014.

Labour MSP James Kelly said: “It’s a case of Alex in wonderland if the SNP think they can try and convince Scots that the pound in their pocket doesn’t matter.

Alex Salmond’s approach on currency is to ignore and hope nobody notices. It won’t wash.

“His failure to answer the most basic questions on currency was one of the key reasons he lost the referendum in 2014. Two and bit years on he still has no answers.

“Scotland is divided enough, the SNP should rule out another divisive referendum.”

Tory Dean Lockhart added: "As the last independence campaign showed, the currency question was one of the most important issues for voters.

“The SNP were at sixes and sevens on it then, and judging by Alex Salmond’s comments they still are now.

“It’s no use trying to talk about trade if you don’t have any concrete plans for what currency you would be trading in."

Mr Salmond said if the UK Government rejected Ms Sturgeon’s bespoke Brexit plan, it was “very likely” there would be a second referendum and, if so, the “likely timescale” was autumn 2018.

Despite a third of Yes supporters voting to Leave the EU, he predicted such people would make independence their top priority if it came to the crunch.

He said: “I would be very confident that the progress we’re seeing in support for independence can continue if the campaign is pitched in the right way.”

He also said there should be another cross-party pro-independence campaign next time, although there were also “lessons to be learned from the first campaign”.

The Yes Scotland campaign had be to be bailed out by the SNP with £825,000 after going broke and being unable to pay its bills at the close of the 2014 campaign.

Scottish LibDem leader Willie Rennie MSP said: “The SNP is paralysed by the independence issue. They are so focused on breaking up Britain that they have completely failed to deal with the challenges in our economy, education and health service.

“A vote in autumn 2018 will only lead to a further 18 months of paralysis as they continue to pursue their independence agenda above anything else.”