One of the worst kept secrets in Brussels is that Nicolas Sarkozy and Angela Merkel don’t exactly hit it off. The German chancellor is even-tempered, precise, methodical. The French president is passionate, impulsive and "an unguided human missile", to quote one diplomat who has seen him in action amd whose jaw has only just started to return to its normal position.

The areas of disagreement between Merkel and Sarkozy, the EU’s most important pair, start with monetary and exchange rate policy. He is scornful of the European Central Bank’s anti-inflation emphasis, but she dislikes his jabs at the ECB’s independence. They end with Turkey, where Sarkozy flatly opposes Turkish entry into the EU and Merkel, though not personally in favour, believes the EU should honour its pledge to Turkey to continue membership talks.

As I watched the European Union’s leaders sign the Lisbon reform treaty on Thursday, my mind wandered back to that pleasant autumn day in Rome in October 2004 when many of these same leaders signed the constitutional treaty that was the present document’s ill-fated predecessor.

Italy’s prime minister at that time was Silvio Berlusconi, the billionaire media magnate. He had fought tooth and nail to make sure Rome was the city in which the constitutional treaty was signed. In fact, some said  this had been the only goal that he really felt passionate about when Italy held the EU presidency from July to December 2003.