The invitations to the European Union’s 50th birthday party went out months ago, and no unimportant detail has been overlooked. No important question, by contrast, has been settled.

Berlin, Europe’s “capital” for the six months of Germany’s EU presidency, will echo this weekend to the music of 27 discos, and 27 cakes are to be baked by cooks from every member state (Britain’s offering, unfestively, will be of the Eccles variety). At vast cost, a Polish designer has come up with a slogan for the party, in all EU languages: “Together since 1957”. Not only is this upliftingly original thought spelt out in the sort of cute multicoloured typography you would expect to see in classrooms for children with acute attention deficit disorder, it also bears no relation to historical truth. In 1957 and for more than 30 years thereafter, ten of the EU’s current members were locked in a living hell behind the Iron Curtain.

The EU’s greatest single cause for celebration is that this is no longer so, that it is now a union for “Europe whole and free”. This was surely an opportunity to remind people of the inspiration that the EU has been to Europe’s new democracies. In Brussels and EU capitals, bureaucrats and politicians agonise at the indifference bordering on hostility with which their publics regard “Europe”. Yet, time and again, they forget about the messages — such as Europe’s identification with individual liberty — that could rekindle enthusiasm.

The body launched with six members half a century ago by the Treaty of Rome has been more enduring than its founders could have imagined. But with longevity has come a lumbering, self-important and, in the eyes of most Europeans, irksomely meddlesome Brussels bureaucracy. Europeans take peace for granted, and no longer associate the EU with prosperity. Many view the euro with distaste, and see the single market not as an opportunity but as a threat to their jobs. These are the political challenges Europe’s leaders need urgently to address.

At 50, the European Union is overweight and badly dressed. The lady will not get over the midlife crisis she has been going through since 2005, when French and Dutch voters rejected the proposed EU constitution, unless the Union’s leaders can come up with simple, slimline ideas for the future that voters can identify with. Reviving enthusiasm for “the European project” is, supposedly, the aim of the birthday card that Angela Merkel, the party’s hostess, has commissioned. But there is a spot of bother about the content. With less than a week to go before the great day, all that has officially been divulged is that it will be no more than a page long, that it will set out in clear, indeed breezy, language (presumably prose) the achievements, values and future goals of the European Union — and that it will mention neither God nor the “constitution”.

Unfortunately, this does not mean that Mrs Merkel has given up on the idea of resurrecting the EU constitution. She has merely, bearing in mind next month’s French elections, deferred that battle to the Union summit in June. Such indifference to popular preferences has come to be seen as typical of the “Community method”. The constitution is the epitome of Europe de haut en bas, of decisions imposed by elites. It is not popular; it is not necessary; it should be dropped. Voters also deserve a political pledge that they will be consulted on whatever institutional changes are proposed in its place. The EU will not inspire affection until it inspires trust.