Gordon Brown will face only one difficult and immediate foreign decision when he takes over – what to do about a new European Constitution (although one part is easy – not to call it that).

Iraq and Afghanistan, the battlefields which Tony Blair has bestowed on him, present no such problems. In Iraq, he can stick happily with Blair’s plan to slither out; Afghanistan has put Britain in a nasty predicament, but there is no urgent need to change course, or even an early change to do so.

But on Europe, we are entering a few weeks of intense wrangling which could set the rules and shape of Europe for a decade. The Prime Minister-elect will have to decide, even before he has taken office, what most matters to Britain and what he is prepared to concede.

“Gordon Brown faces a difficult choice,” said Charles Grant, of the Centre for European Reform, yesterday. “If he does sign up to something that looks like building a European super-state, then he will be under massive pressure to have a referendum. But if he doesn’t, he loses the chance to be part of the new pragmatic, liberal team of leaders that will steer Europe over the coming years”, including Nicolas Sarkozy, the new President of France, and Angela Merkel, the German Chancellor.

Would that matter to him? Surely a bit. True, Brown’s reputation in Europe is hardly one of clubbability. Other European governments, now trying to discern his views from his past behaviour in finance ministers’ meetings, have an impression of big-shouldered abrasiveness, and a desire to take Europe to task for its financial self-indulgence, beginning with its farm subsidies.

On the other hand, it would be hard, when it looks as though the new kids on the block are taking over the club, to turn down a chance to join. Tony Blair, when just elected in 1997, teamed up with Romano Prodi, the Italian Prime Minister, and then Gerhard Schröder, when he arrived as German Chancellor in 1998, to spin out their Third Way theories for the centre Left, sweeping Bill Clinton on to their conference platforms too.

But between Brown and any such alliance is the task of striking a deal with the other 26 members on a new treaty to steer the European Union. The only point on which they agree is that it should not be called a Constitution, to put as much distance between it and that ill-fated, 400-page effort of 2004. Britain’s closest allies are France and the Netherlands, which rejected that text in referendums. Brown aides expect to have a close relationship with Sarkozy, and Geoff Hoon, the Europe Minister, was in Paris yesterday and will be in the Netherlands on Thursday.

Even though a deal – if there is one – would be thrashed out before Blair steps down, the formal agreement would not be until autumn, in Brown’s premiership, and the two have worked closely together in setting Britain’s position. They cannot accept, their aides say, anything that granted significant new powers to Europe, because that would push the Government towards holding a referendum (which it could confidently expect to lose).

Britain may want to ask for exemptions on justice and constitutional affairs, if these were to be prescribed by “qualified majority voting”, although it has not yet made a formal request. It is also very keen to see a change in voting rules which would give more weight to its large population. Poland is not, but that will be a test of Merkel’s charm on Lech and Jaroslaw Kaczynski, the twins who head the Polish Government.

If Brown, with Sarkozy’s help, can navigate these obstacles, then he will have won a place on the steering committee of a club of enviable status but suprisingly light obligations. If he fails, he will be blamed for the rows and paralysis – and the end of the project of enlargement – which will persist throughout his time at No 10.

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