The new French President was greeted in Berlin last night like an old friend. For a moment it seemed as if the Franco-German partnership, the engine that has powered the integration of Europe for 50 years, might splutter into life again.

Only minutes after hugging each other on the red carpet — it seems that hand-kisses are as much of the past as Jacques Chirac — Angela Merkel, the German Chancellor, and her guest got down to the business of the European constitutional treaty. Mrs Merkel has only six weeks before the final summit of her EU presidency and is determined to get the broad outlines of a deal in place. And France, she made clear, is now central to the mission.

“I am sure that we will work together very closely,” said Mrs Merkel. “The gesture you have made, coming here so soon after becoming President, makes clear that Germany and France not only need each other but are friends.”

Mr Sarkozy, who spoke English with the Chancellor when no interpreter was on hand, emphasised the urgency of his tasks at home and within Europe — hence the sprint to Berlin. “I don’t believe there is any sense in waiting before tackling problems. They do not get any easier for delaying them.” But for Mrs Merkel, the arrival of a more assertive French leader is not all good news.

As President of the EU, Mrs Merkel has resuscitated the European constitution from its death-bed — largely because the French presidency has been too weak and too distracted to trip her up. A strong French President changes the internal dynamics of the EU and may sap the bargaining authority of Mrs Merkel.

“To win in a team game you need all the players on the field,” said Ms Merkel before her guest touched down. This was a reference not only to the absent French but also to the imminent handover of power in London.

That a new French leader makes his first foreign trip to Germany has become a post-war tradition. But Franco-German political friendships have functioned best when the leaders come from different ends of the ideological spectrum. Helmut Schmidt was a Social Democrat, Valéry Giscard d’Estaing was a conservative: Helmut Kohl was a Christian Democrat, François Mitterrand a Socialist. The two current leaders are of the centre-Right. That will make certain issues simpler: there is broad agreement on transatlantic relations, a shared suspicion of Vladimir Putin, a reluctance to allow Turkey into the European Union.

But these common positions may end up magnifying the very real differences about state intervention and the indepndence of the European Central Bank. “Merkel will not rally to Sarkozy’s agenda on reining in the European Central Bank, fighting tax competition and developing an EU-wide industry policy,” says Martin Koopmann, an EU expert at the German Council on Foreign Relations.

Mrs Merkel and Mr Sarkozy remain very different personalities. The German leader has nothing of the showman about her. Moreover, she will be increasingly constrained by her coalition with the Social Democrats, which is pushing for a more social Europe, and closer ties with Russia. All that is likely to introduce tension into the working relationship with Nicolas Sarkozy.

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