A separate currency is the prudent option for an independent Scotland to give it the powers needed to manage any future financial shocks, according to economic experts.

The Scottish Government's proposal to keep the pound in a currency union with the remainder of the UK would deprive Scotland of the powers necessary to adjust the exchange rate or interest rates to steer its way through another economic crisis, the experts said.

National Institute of Economic and Social Research (NIESR) has teamed up with the Economic and Social Research Council to assess currency options for an independent Scotland.

Scotland would start life heavily in debt to the tune of £153 billion, or 86% of what it produces including oil, although this is lower than the UK's projected 101% for 2016-17, according to the experts.

It could sell all of its oil to the UK to reduce its debt and rid itself of a volatile resource, the experts suggest, but this would push the deficit in what Scotland produces and consumes even higher.

Scotland must face up to the debt to have a chance of becoming a successful, small, independent country like Sweden, Denmark or Norway, the experts said.

NIESR director of macroeconomic research Dr Angus Armstrong said: "Countries throughout history have considered how you reduce your fiscal burden. You either tax people, spend less or sell your assets. We recognise that selling assets is politically difficult and sensitive, but it's only because nobody is talking about the debt."

There is no "free lunch" for Scotland whatever constitutional or currency option it chooses, as either way it is in for varying degrees of "painful" austerity, the experts claim.

"It would be prudent for the Scottish Government to retain the policy levers by introducing its own currency, which you would then tie to the pound. That, of course, is a complex thing to do and there are transitional risks," Dr Armstrong said.

"Reasonable people can disagree on this, but the approach we are taking is risk management. We don't know what the negative shock could be but with this sort of profile you would like to have a degree of freedom to move.

"That is not really a free lunch because it would still be very difficult. You would have to establish your credibility, and you need to have a stabilisation plan in place for achieving this."

The coming years will be economically painful whatever the constitutional situation, according to Dr Armstrong.

"Our objective is to avoid big welfare losses and minimise the negatives," he said.

"There are several example of countries with Scotland's level of income and population which are perfectly successful and in Europe. Denmark, Sweden and Norway all have their own currency. What they all have in common is low debt-to-GDP ratios.

"So the question is: how does Scotland go from the starting point in 2016 to the position of these very successful countries? Can you be like this and have your own currency? Of course you can, just look at them. It's not obviously had any huge disadvantages using their own currency.

"They tie them to the euro, and Scotland would be tied to sterling. But having their own currency allows them in such circumstances to make adjustments, which they have done."

The experts are sceptical about the SNP's plan to put money into a Norway-style oil fund, insisting "you can only spend the oil money once".

They said: "It can either go in the oil fund, it can go to pay down your debt, or you can go and spend it in your fiscal accounts, but you can't have it three ways."

There is "merit" in the option of selling Scotland's oil assets, the experts said.

"You could start off with a much smaller debt-to-GDP ratio if you swap the assets to repay the debt.

"You've got a huge asset there that is very volitile, and debt which is pretty certain. Your interest payments are going to be pretty steady every year.

"One option is to say: why don't we sell this and reduce the debt and then start off in totally different position?' If you sell the oil to the UK, you don't have to worry about this debt. There's a big way to make this problem simpler.

"What does Scotland get? Oil is very volatile. When the price is high it's terrific but when it's low it's difficult. By getting rid of that volatility, which is much more easily handled by the UK as it is a smaller part of its economy, it would make Scotland's budgeting simpler.

"The disadvantage is that your deficit once included oil but now it doesn't, so now your budget deficit really is big."

Dr Armstrong urged the Scottish and UK governments to set out their respective currency and debt management plans before the referendum to give voters a realistic picture of the problems each constitutional position would present.

The experts have also summarised their currency options in an eight-minute cartoon which is available on YouTube.