So Scotland now has a greater deficit than the rest of the UK.

Is this a "landmark moment in the debate", as Better Together leader Alistair Darling claimed yesterday? It is certainly one that neither side will forget in a hurry.

The Scottish Government and Yes Scotland have not held back from using evidence in any given year of Scotland's smaller deficit to make the case for independence. John Swinney, the Finance Secretary, said on the strength of last year's figures that every Scot was better off by £824 because of it and this statistic has been used repeatedly to make the case for independence, including by fellow minister Nicola Sturgeon (though it was later revised down to £489).

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Pro-independence campaigners have also made a play of figures that last year showed Scots contributed more in tax than they received in public spending, claiming Scotland had a raw deal from the UK.

So what are voters to make of news that Scots now carry £283 more debt per person than the rest of the UK? Or the fact that 9.1% of UK revenue was raised in Scotland in the last financial year but Scotland accounted for 9.3% of public spending? Hard done by? Not any more, apparently.

For the Yes campaign, "bigging up" the earlier figures might start to look like a tactical error as oil revenues fall. Voters may have been confused to hear two different sets of statistics discussed yesterday.

The first lot show the gap between revenue raised in Scotland (including a measure of Scotland's share of North Sea oil and gas revenues) and public spending (both "current spending" on the cost of public services, and capital expenditure), the most rounded view of Scotland's finances. They show that Scotland has a deficit of 8.3% compared with 7.3% for the UK, a reversal of last year's position.

Mr Salmond focused instead on the gap between revenue raised and current spending alone, leaving out capital spending. It, too, showed that Scotland had a bigger deficit than the UK though only by 5.9% compared with 5.8%.

He also highlighted the five-year average deficit which for Scotland was 4.3%, compared with 5.9% for the UK, claiming that this was reasonable because the SNP intends eventually to start paying into an oil fund to iron out year-on-year fluctuations if Scotland votes for independence.

It is striking that ministers did not feel the need to focus on longer-term trends when the year-on-year figures were more convenient.

There are specific reasons for the latest deficit figures. They are affected by events that are unlikely to be repeated every year, but they nevertheless highlight how exposed Scotland's public finances are to fluctuating oil revenues. This year the drop is caused by disruption to production and high levels of investment; next year it could be falling oil prices.

The debate about the finances of independence will continue, but this latest Gers report should serve as a cautionary tale for the Yes campaign not to overplay statistics.