There was much heat generated by yesterday's competing claims on the costs and benefits of Scottish independence, but precious little light.

Both sides claimed their preferred option would leave Scots better off and sought to undermine the assertions of their rivals. According to First Minister Alex Salmond, everyone would be richer by £1,000 a year in the event of a Yes vote. Not so, according to Danny Alexander, Chief Secretary to the Treasury. Independence would make Scots worse off while staying in the Union would provide a UK dividend of £1,400 per person per year.

They cannot both be right and, indeed, both reports are based on projections and assumptions that might be proved untrue in time. Neither side knows precisely what the economic conditions will be on the point of independence and in the first years of a new state.

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Even so, there are some issues that are emerging as crucial economic measures in the debate. The first is the set-up costs of a state and the Treasury suffered some self-inflicted damage by claiming the cost of a new state could be as high as £2.7bn. Professor Patrick Dunleavy of the London School of Economics said his research, which formed the basis of the claim, had been manipulated to make the costs look many times larger.

It was a bad mistake by the Treasury but, equally, the error cannot hide an important fact: setting up a new state will be expensive and the Nationalists have still to come up with their estimate. They should do so promptly and explain how the figure has been calculated.

The second central issue is oil revenues. These form a pillar of the Scottish Government's positive projections. New technologies have opened up reserves that were previously unreachable and the Scottish Government's forecasts are more generous than the Treasury's. But the general picture is one of decline in the medium term.

The Scottish Government says it would establish an oil fund which, had it been started in the 1970s, could make a substantial contribution to the economy at present. Whether such a fund has the same potential if started now, when there is much less oil and gas to exploit, is open to question.

The third important battleground is the potential fiscal deficit: the difference between spending and tax income. The Treasury says that, over the past 15 years and assuming a geographical share of North Sea oil and gas, Scotland's fiscal balance has averaged minus 3.8 per cent but the question is whether a change in policy in an independent country could reverse this. The Scottish Government says the population will grow through immigration. More people means more tax income. But spending is just as likely to increase because of Scotland's ageing population and whether the population could be made to grow sufficiently to compensate is uncertain.

There are many other factors at play that increase the uncertainty, such as the proportion of shared assets Scotland would be entitled to and share of debt it would take on. These and other factors could be resolved only in negotiations between the UK and Scottish governments after a Yes vote. But both sides must do all they can to bring clarity to the debate before then, for one simple reason: the referendum will be won or lost not just on emotional grounds but on economic ones too.