'BE afraid: be very afraid!" That was a trailer for a horror movie back in the 1970s. But recent events in the real world have made it a motto for all of us. I refer specifically to the United States government's decision to withdraw 70,000 of its troops from Europe.

For the Americans, this makes perfectly sound military and political sense. Those troops were stationed in Europe to counter the Soviet threat. Now that communism has collapsed, no such threat exists. There is a new threat and it is called Islamic terrorism. And to meet this threat the US is sensibly re-inventing its global strategy and redeploying its forces so as best to counter it.

Perhaps you will extend to me, your Tuesday columnist, a measure of sympathy, for I am caught between the proverbial two stools: on the one hand I feel compelled to spell out a grave and present danger; but then I know from experience that what I say will be misinterpreted by those who will do anything rather than see things as they are.

So I must preface my remarks with a health warning: I do not think that all Muslims are inclined to terrorism. Most devotees of Islam wish to practise their religion in sincerity and live in peace but the atrocities of the last few years show that the dominant force in Islam worldwide seeks supremacy over the West and will use any means to achieve it.

But while the US shows every sign of ordering its resources to counter this threat, Europe looks increasingly like a political entity on the point of caving in to it.

The old Europe which for centuries led the world with its Christian values is now decadent and moribund. Islam, by contrast is resurgent and full of zeal.

Muslims believe in the moral law. They teach - with scant regard for Western superstitions such as non-sexism - their boys the Koran which they interpret fundamentally as a practical guide to daily living.

But European civilisation has become secular and ultra-permissive. We are no longer guided by the Bible and church doctrine; and our ancient institutions - the law, parliament and the monarchy - have been catastrophically weakened by our obsession with "modernisation" and "inclusivity".

Muslims believe in God, fervently. They insist on the authority of the moral law. But the pervasive trend in modern Europe is atheism. Mosques are being built by the score while Christian churches are being closed down by the hundred.

Muslims look to a godly authority beyond individual opinion. But Europeans have embraced rampant consumerism, and mass pleasure-seeking: drugs, voyeuristic TV shows, football, clubbing and the mindless cult of celebrity.

The birth rate among secular Europeans is falling. Among Muslims it is rising swiftly, while at the same time we are seeing Muslim immigration on a scale unprecedented. The likelihood is that Europe's decadent civilisation will be overcome by resurgent Islam. This is my message. I beg you, please don't shoot the messenger - but do examine the message.

* Peter Mullen is Rector of St Michael's, Cornhill, in the City of London, and Chaplain to the Stock Exchange.