LONDON BRIEFING: As the war with Iraq starts to disappear from the front pages, it is tempting to quote Winston Churchill's famous speech delivered after the First World War, when he reflected on a world utterly changed, apart from "...the dreary steeples of Fermanagh and Tyrone emerging once again".

It is tempting not only because of the obvious parallels with the stalled negotiations in the North, but also because there is another dreary and seemingly never ending quarrel, which has already hit the post-Iraq headlines. The great euro drama is back and the leading actors have not changed - but some of their lines have been rewritten.

The serial cabinet seat resigner, Peter Mandelson, has caused a stir by writing, in the Sun, another passionate pro-euro polemic. He hinted that the success of the war in Iraq, in the teeth of so much opposition, is now the model for the euro. Having overcome the antipathy to war of the public and a great swathe of the Labour party, persuading them of the virtues of the single currency will, according to this line of reasoning, be a piece of cake.

Now, Mr Mandelson is still a chum of Tony's, and the big question this week has focused on whether the prime minister gave the article his blessing. Gordon Brown, the chancellor, apparently choked on his cornflakes when he heard about all of this while safely - from Mandelson's point of view - out of the country. With the prime minister's chief spin-doctor distracted by exertions incurred while running the London marathon, there was no chance of an early retraction or clarification. Conspiracy theories have been running ever since.

The chancellor has, apparently, already concluded that the time is not yet right for Britain to join the euro. The single currency has failed his famous five tests. The definitive assessment of those tests is due to arrive in a few weeks and is said to run to 2,000 pages of dense economic analysis. Most of us could do it using a lot less paper.

Economically, Britain is already doing better than Europe. Politically, we are hardly singing from the same hymn sheets as Germany or France. Why we need more than that is hard to see, but Mr Brown clearly needs to impress us, again, with the size of his intellect.

I find it tough to imagine the average Sun reader being impressed by Gordon Brown doing algebra. Indeed, given the complaints from British industry about the state of maths education in particular, it is hard to spot who will even read the chancellor's epistle, let alone understand it.

So if Mr Blair is to nevertheless press on for a referendum on the issue, there will almost certainly be the small matter of Gordon Brown's resignation. Given reports in some parts of the media that the foreign secretary, Jack Straw, is to be rewarded for his performance during the war with promotion to chancellor, some people think Mr Blair has anticipated Brown's departure already. Some conspiracy theories are more fanciful than others.

Could Britain be persuaded to vote for the euro? Are Tony Blair's powers of persuasion that good? There is the slightly inconvenient fact that the euro's popularity has sagged even more following the row with Germany and, in particular, France. There is also the more significant fact that Gordon Brown is right: the UK economy would be placed in harm's way if we adopted the euro.

Nevertheless, the prime minister, always more convinced about the politics rather than the economics of the single currency, might be tempted to go for it. In a funny kind of way, the prime minister's approach is the correct one. It is virtually impossible to envisage the British economy ever being obviously ready for the euro and the decision will always be a political one.

Gordon Brown's 2,000 pages notwithstanding, economic analysis can never provide the definitive judgment, relying as it does on two sets of inherently uncertain forecasts. One set has to forecast the path (forever) of the economy without the euro, the other with.

Meanwhile, British industry is quietly celebrating sterling's slide against the euro, as the rise of the single currency adds to Europe's woes. The weakness of the euroland economy should be enough to give pause for thought for anybody thinking of giving up control of the domestic economy, even Tony Blair.

Chris Johns is chief strategist with ABN Amro Securities, London. All opinions expressed are entirely personal.

cjohns@eircom.net