Predictably, John Swinney reached for the most reassuring numbers he could find when the cabinet secretary for - among many other things - sustainable growth commented yesterday on the latest GDP numbers.

An increase of 0.9% in Scottish output in a single quarter is unusually robust. When the UK as a whole only manages 0.6% over the same three-month period, it's tempting to project it as "a welcome and positive piece of news in the current climate". As Swinney duly did.

But that is far from the whole story. Now that we have the complete Scottish growth picture for 2007, it is clear that, in its central economic ambition to match UK growth by the end of this parliament, our minority SNP government is actually going backwards.

In 2006, Scottish GDP rose by 2.6%, just a whisker shy of the 2.7% recorded for the UK economy as a whole. Last year, annualised Scottish growth fell to 2.2%, while UK growth increased to 2.9%. So, despite a good final quarter, the growth gap is, as the SNP might have painted it - were it still in opposition - seven times as big as it was a year ago.

Indeed, over all eight quarters of 2006 and 2007, the latest annualised Scottish growth rate (2.2%) has been exceeded five times. And one of the two quarters where annualised growth was even lower was during the previous three months, when the SNP was also in power and growth hit just 2.1%.

Swinney sought further comfort from Scotland's financial services sector, "buoyed by the highest ever quarterly growth in banking". But the growth story there is deeply perplexing. And even if the published numbers are credible, future prospects, including what is currently underway at Scotland's biggest company, RBS, look a great deal darker.

Remember what was already happening in financial markets in the final three months of last year. With the fall-out from the global credit crunch intensifying and Northern Rock on the rocks, we are asked to believe that, while financial services as a whole in the UK grew by just 0.9%, in Scotland they powered ahead by 4.6%.

By contrast, over 2007 as a whole, output from Scottish financial services grew less than half as fast (by 2%), while the comparable UK figure was apparently 11.1%.

Scotland's banking sector, which accounts for more than half of all our financial services, supposedly grew by 9.3% in that final quarter, having contracted over the previous two. But if it did, and the whole sector grew by 4.6%, the rest of the sector must have been contracting quite sharply at the year end.

Analysts at CPPR, the Centre for Public Policy for Regions, point out that, while the financial sector is very important to the Scottish economy, it is difficult to collect good data, on two counts. First, it is difficult to come up with an accurate measure of output. Second, in an economy where two major banks and a large insurer, with extensive UK-wide interests and growing international reach, dominate the sector, it is difficult to apportion profit shares to specific geographies.

The Centre has wider concerns about the reliability of current Scottish growth data. It points out that, on the measure of output used for UK regional accounts, Scotland was already growing faster than the UK as a whole, in 2004, 2005 and again in 2006.

However, on the measure used by National Statistics to compile the Scottish government's quarterly GDP numbers, underperformance has been the norm. And, as we have seen, despite a near catch-up in 2006, the gap widened again last year. CPPR is right to call again for a comprehensive review of the data used to measure Scottish growth.

On that the SNP government has remained silent. In opposition, Jim Mather was a vocal critic of the methodology of the current GDP series. Mather claimed the regular updating of the weights given to specific sectors was designed to write past underperformance out of the script and, if anything, flatter the Scottish economy's performance over time.

While making catch-up with the UK growth rate by 2011 the centre-piece of their economic strategy in office, Mather and his colleagues have been silent on methodology since last May. There again, last April Mather told the Financial Times: "Raising income tax rates would be naive in a knowledge economy".

That hasn't stopped the SNP government pushing ahead with its additional 3p on all income tax bands for workers to help pay for the abolition of council tax.

When the SNP first launched its pledge to match UK growth by 2011 and then aspire to match the average growth of small, independent European economies by 2017, put at the time at around 4%, one political cynic told me: They might just make their first target if the UK goes into recession.

Well, short of that, they may find that retrenchment in financial services in the wake of the global credit crunch may leave Scotland even further adrift of their target by the time we get to review our 2008 performance, next April. And, by then, we will be only two years away from the next Holyrood elections. How might that be explained? They could always blame London, I suppose.