GORDON BROWN should become Foreign Secretary after the election. That is in both his and Tony Blair’s interests. For once, there is a coincidence of Mr Blair’s desire to establish his legacy and Mr Brown’s for a benign inheritance.

The link is next year’s referendum on the European constitution. This is mainly seen just in terms of Mr Blair’s future. But, for Mr Brown, taking over as Prime Minister after a defeat would be the worst possible start to his premiership.

The EU referendum is often discussed as if it were just an optional extra to the main political debate. Labour will not highlight Europe in its election campaign. Instead, it will concentrate on the strength of the economy and public services. This is in the hope of retaining the support of Eurosceptic newspapers and voters now, with the promise of a separate, freestanding vote on Europe later.

But Europe cannot be ringfenced. Relations with the EU are as central to politics as public services, particularly given Mr Blair’s repeated promise that Britain should take a leading role in the EU. These early hopes have been tarnished by the rows over Iraq and by the indefinite delay of euro membership.

There are some positive developments: notably a greater focus on the EU’s competitive position. After the waffle of the Prodi years, José Manuel Barroso, the Commission President, has made a priority of stronger growth, job creation and deregulation. His five-year work programme and the relaunch yesterday of the Lisbon reform agenda sounded like any speech by Mr Blair or Mr Brown. This is hardly surprising given the input from Peter Mandelson. But the president of the European Socialists has complained that this is little more than “a thinly disguised neoconservative agenda”. Of course, good intentions are not the same as action. But, at least, the words are right.

The key is the EU constitution. This is more than “tidying-up” — a stupid phrase. But, equally, it is not a centralised European state. It is a compromise between closer integration to take account of enlargement to 25 members and the retention of an intergovernmental approach elsewhere. Much of the media coverage has been grossly distorted, creating bogus fears (about the loss of Britain’s veto over taxation and the deployment of troops), or objecting to EU powers agreed long ago.

The constitution is viewed very differently on the other side of the Channel. The unsuccessful anti-constitution side in the French Socialists’ debate three months ago argued that it is a victory for a “British Europe”. The divide was apparent again yesterday when Michael Howard and Angela Merkel, of the German conservative Christian Democratic Union took sharply opposed views at a lunchtime discussion organised by the Konrad Adenauer Stiftung.

The biggest divide is over the consequences of a “no” vote. Mr Howard presented this as an opportunity: a chance for different countries to go their own ways on closer integration, while remaining full members of the EU. As some leading pro-European Tories muttered, this is a fantasy.

A “no” vote would not just mean a reversion to the status quo, especially if all, or virtually all, other EU members back the treaty. France and Germany would probably attempt to create a core Europe, with Britain on the outside. As Sir Stephen Wall, Mr Blair’s former European adviser, has said, it could be like the eurozone, where all countries bar Britain meet together to take the main decisions before formal meetings. It is no good Mr Howard saying “good luck to the rest”. Britain would, in effect, become a marginal member of the EU. A “no” vote would also fuel demands within the Tory party for withdrawal.

For Labour, not only would Mr Blair almost certainly have to resign as Prime Minister after a “no” vote, but Mr Brown would have to spend the rest of the Parliament renegotiating Britain’s position in the EU. He could not just dismiss the constitution as Mr Blair’s agenda. Despite differences of language, Mr Brown is no Eurosceptic.

The odds against winning remain high. No opinion poll has shown a majority in favour, and support in Britain is less than in any of the other 24 countries. However, two polls last weekend showed margins against of just three to ten points. There are also many “don’t knows” and “persuadables”, so opinion could shift, but only if the case is made repeatedly from now onwards.

At present, the pro side is hampered by Mr Blair’s reluctance to take a high-profile lead. Jack Straw has given warning of the danger of a “weaker and isolated Britain whose future prosperity and security is put at risk”, and Denis MacShane, the Europe Minister, has, as ever, been energetic. There has largely been silence from other ministers. There are even murmurings that the referendum will be delayed from March or June 2006 to the last possible date of September next year. One spurious reason is that Mr Blair could not start campaigning until after the end of the UK presidency of the EU in the second half of this year.

The only way that the “yes” side can win is if all ministers are fully involved. It would be fatal if the vote were seen just as a way of getting rid of Mr Blair. Mr Brown could, and should, play a leading part, not least in helping to reverse the increased opposition to the constitution among businessmen. The best way for Mr Blair to tie Mr Brown into this campaign would be by making him Foreign Secretary. This might also strengthen his appeal as a potential prime minister by demonstrating the diplomatic skills he has recently shown in Africa.

Mr Brown needs a “yes” vote, in the interests not only of a smooth start to his premiership, but also of avoiding a damaging disruption both to Labour’s foreign policy goals and to Britain’s long-term strategy towards Europe.

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