America’s third-quarter GDP data was every bit as good as Britain’s, published last Friday, was awful.

Growth of 3.5 per cent from July to September, marking an end to the worst US recession in 70 years, was better than anyone in the market dared hope for and, coupled with some strong results from Colgate-Palmolive and Procter & Gamble, lifted Wall Street sharply.

Yet drill deeper into the numbers and the picture is not quite so optimistic. For a start, more than two fifths of output growth during the quarter came from the motor sector, directly as a result of President Obama’s “cash for clunkers” scheme. That has now expired, as will another significant contributor to growth during the quarter, the $8,000 tax credit for first-time home buyers. Another big contributor to growth during the quarter, higher defence spending, cannot be relied upon to continue at the current rate either.

The same applies to restocking, which accounted for just over a quarter of the growth in output seen during the period. That had to happen eventually, given the extreme levels of de-stocking that had been seen in the previous year, which had led to unusually low inventory levels. America’s factories may be kept humming for another couple of quarters, as inventories are replenished, but there are already fears that this may peter out towards the middle of 2010.

There are other reasons to be sceptical about the strength and duration of any uptick in growth. America’s households remain deeply in debt — indeed, one of the reasons growth was apparently so robust during the last quarter was that savings ratios fell again as consumer spending rose — and ultimately, this will severely hamper the recovery. It is also worth bearing in mind that business investment, a prerequisite for job creation, continued to fall during the quarter.

That said, it would be churlish to carp too much, particularly since the Obama Administration’s efforts to stimulate the US economy have conspicuously been more successful, for example, than the UK Government’s daft VAT cut or its paltry temporary reduction in stamp duty for house purchases.

One further cause for optimism came last night when a Federal Reserve economist pointed out that inflation expectations among Americans are close to an all-time low. That, along with low levels of capacity utilisation, means there is plenty of scope for US interest rates to be kept at their current low levels for some time to come.

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