We appear to be witnessing one of the most serious reversals in British foreign policy since the Second World War. John Major's government may be on the verge of capture by nationalists who are opposed to the long-established aim of integrating Br itain into a community of European states.

This policy, set in place in 1973, arguably represents the most important constitutional change in this country since the Glorious Revolution of 1688. It laid out a new path for Britain after it had lost its empire and as it sought to retain influence ina world dominated by large power blocs.

Only a few years ago, the policy of working ever more closely with neighbouring European states seemed unassailable. Complaints about waste by Brussels were general, but critics sought to reform the Community not to isolate Britain from it. A few politicians argued that Britain should leave, but these radical voices belonged to marginal figures. No more.

As each day goes by, the Prime Minister shifts his policy further towards those seeking to freeze development of the Community. Douglas Hurd, the chief advocate of a pro-European policy, looks increasingly isolated as colleagues scheme against him. The Foreign Office faces humiliation.

The nine whipless Tory MPs may seem to be relatively insignificant. But their message - the logic of which demands British withdrawal - is now attractive to many fellow MPs. They have shifted the centre ground not only in the Tory party at large but among Cabinet ministers. Their campaign has been fuelled by its considerable popular appeal.

There is a sense of panic among those political figures who supported two decades of Britain's rapprochement with Europe. In today's Financial Times, Lord Howe states that UK foreign policy is "being dragged into a ghetto of sentimentality and self-delusion".

This is obvious to anyone taking the briefest look at what our European partners are discussing. At the weekend, Jacques Santer, the new European Commission President, pressed the case for speedy introduction of a single currency for member states. Edouard Balladur, the French Prime Minister, says that France is able economically and politically to accept a single currency. Meanwhile, Britain labours over the basics of a question that was apparently settled 20 years ago.

Obviously there are difficult issues. The EU's democratic deficit, its failure to address sufficiently the challenge of the rising Asian economies and practical difficulties of monetary union are but three examples. But Britain has nothing to gain by cocooning itself in inglorious isolation. The battle over Britain's relationship with Europe must be won by those who favour constructive engagement.