By Mark Gregory BBC business reporter

The euro still haunts the UK economy

New figures show that France may be about to supplant Britain as the world's fourth largest economy.

The data gives another twist to the diplomatic rivalry between two of Europe's leading powers, which have very publicly taken opposite sides in the debate over support for American action against Iraq.

Britain and France have been quarrelsome rivals as well as neighbours for hundreds of years.

One sign of this is a row about economic statistics.

The debate is more about national pride than economics

Since 1999, Britain has claimed to have the larger economy, as measured by the size of its gross domestic product compared with France. GDP is a measure of the total value of all goods and services.

After decades of post-imperial decline, Britain's politicians have been able to say the tide has been turned, that the country once again has a successful, dynamic economy - ahead of France as the fourth-largest in the world.

France nosing ahead

Latest GDP figures from the two nations, however, show that the scales may soon tip the other way.

That is not because of any change in the relative economic performance - it is due to the fact that the euro, the currency all transactions take place in in France, has risen in value against the UK pound.

If the euro rises another 0.75% against the pound, the French economy will apparently become larger than that of Britain.

Ironically, exactly the same thing happened in reverse four years ago.

Then the pound was strong and the euro weak, so Britain's GDP seemed to get bigger than that of France.