Nick Clegg: We cannot afford to be left out of the new Europe

Why bother? As the debate on the stalled European constitution restarts, once again, after the Christmas and New Year break, Blair can be forgiven for wishing it would simply go away. What with Hutton and tuition fees, he already has plenty on his plate. As long as the draft constitution remains stillborn, he can also happily ignore the clamour for a referendum.

Complicating matters further, Bertie Ahern, the Irish Taoiseach and holder of the EU presidency, declared last week that the understanding that Blair had reached last month with Silvio Berlusconi on the UK's so-called "red lines" was null and void. The prospect of fighting precisely the same battles all over again must fill Blair and his team with dread.

It is little wonder, then, that the Government barely concealed its delight that the Brussels Summit last month failed to reach an agreement on the constitution. Jack Straw made much of his minimalist view that Europe could easily live without a new constitution. Gordon Brown allied himself to the unfounded claims from business lobbies that the constitution was a "threat" to UK competitiveness.

Yet, despite the pressure to turn his back on Europe's constitutional project, it is in Blair's overwhelming interest to re-enter the fray as rapidly as possible. The compelling reason, as so often in politics, is because the alternatives are far worse. If only Straw's blithe assumption that the EU could happily trundle on as before in the absence of a new constitution were true. In fact, without a deal soon, the EU is likely to evolve in ways directly contrary to Britain's national interest.

Consider, first, the position of the EU's principal political powers, Germany and France. Jacques Chirac is notably lukewarm in his support for a new constitution. The emerging political consensus in France is that an enlarged EU will undermine French primacy at the EU's top table, and that the draft constitution would bind France to a dysfunctional decision-making arrangement. That is why there is such interest in a new Franco-German political union. The French political elite has long believed that its strategic interests are best secured by hugging the Germans so close that the rest of Europe will eventually be encompassed in their embrace.

True to form, British commentators have breezily dismissed the French musings on the creation of a new Franco-German "core" as so much hot air. To be fair, there is little obvious substance to many of the proposals so far for a new Franco-German alliance.

Yet, the importance of political will must never be underestimated in EU affairs. The British have a notoriously bad record in misreading the intentions of our EU partners, from the founding of the European Community in the 1950s onwards. Again and again, Britain has found itself condescendingly dismissing the stated aspirations of other EU members, only to find itself playing catch-up when the details subsequently appear both more concrete and serious than the initial rhetoric implied. In this light, the draft constitution serves as the best guarantee available to Blair that the French and Germans will remain locked into a collective EU endeavour. There is an overwhelming strategic interest in minimising the risk of British marginalisation in a European club in which a "hard core" is formed by the French, Germans and others.

The alternative, often heard in policy circles in London, is that an enlarged EU will swell the ranks of close British allies to such an extent that we should have little fear of marginalisation. It is certainly true that, once the EU is enlarged to include 25 members this May, the potential for promiscuous deal making increases substantially. But this should not disguise the fact that many of the UK's natural allies in the new accession countries - such as the Baltic states or Malta - are simply too small to create a meaningful counterweight to the existing EU pecking order. It is also wishful thinking to assume that Poland, Hungary and the Czech Republic, the leading accession countries, will automatically align themselves with all British interests. Other than a general inclination towards Atlanticism, there is no evidence such a durable coalition of interests will arise in an enlarged EU.

The real challenge for Britain is not to duck and weave through a multiplicity of alliances in an enlarged EU, as if European politics had reverted to some military board game, but to make the EU - as a whole - coherent, effective and accountable. Without the constitution, there is a real risk that EU business will simply grind to an unedifying halt, exacerbated by increasing political bickering. If Britain were perceived to connive in such a dismal outcome, the long-standing British objective of a wider, open European club will have been discredited for good.

It is vital, for Britain's own defensive interests and for the efficacy of the EU, that Blair should urgently re-engage with the negotiations for a new EU constitution. As always with European policy, it will carry real domestic political dangers. But Blair claims to understand that, on such vital matters, leadership must be exercised if Britain's place in Europe is to be secured. Now he must prove it.

Nick Clegg is a Liberal Democrat MEP