Twenty-two months ago I stood in the rubble of what had once been the fine perimeter buildings and courtyard of Pera House, the British consulate-general building in Istanbul. A few hours before, it had been blown up by Al Qaeda-linked suicide bombers. Sixteen people were killed - three British and 13 Turkish citizens.

Alongside me that somber evening was the governor of Istanbul and my friend, Abdullah Gul, Turkey's foreign minister. I had many emotions, but one was of the reassuring, uncompromising solidarity I was offered by the Turkish government and people; the other of how familiar - yes, European - Istanbul felt; how close together we were despite the efforts of the terrorists to divide us.

I've often thought of that day during our many discussions about Turkey's longstanding application to join the European Union. As the Oct. 3 date set for the start of negotiations toward full membership approaches, it is worth underlining Turkey's strategic importance and the momentous consequences that will follow from that decision.

In school I was taught that the boundary between Europe and Asia went straight down the Bosporus, through the middle of Istanbul. Of course, "Asian" influences in Turkey are strong, just as "North African" influences are in Spain or Italy.

But we in Europe long ago decided where we wanted Turkey to be anchored. In 1952, we - the United States, Germany, Britain, France and others - invited Turkey to join the North Atlantic Treaty Organization. In 1963, Turkey signed an association agreement that led to a Customs Union with the European Union.

That agreement held out the prospect of EU membership. In 1987, Turkey applied, in 1999, it was granted candidate-country status, and in 2002 the European Council decided that it would open accession negotiations once Turkey had fulfilled the political criteria for membership.

These decisions by the European Council about Turkey have been about nothing less than the kind of Europe we are creating. There are now two options: a Europe turned inward on itself or a Europe looking outward to the rest of the world; one that expands its boundaries to build a wider community of stable, prosperous democracies or one that closes the door to its neighbours.

We don't have the luxury of choice. We live in a world of global challenges and global competition. A static Europe will not face either with confidence. Stopping enlargement would only weaken Europe's ability to compete with emerging Asian economies.

And enlargement has been good for new member states and the EU as a whole. For Spain, Portugal and Greece in the 1970s and 80s, for East European countries in the 1990s, both the prospect of membership and then its reality have acted as a powerful motor for change. When some of these new members began their talks they were far short of the membership standards. They transformed during that process, just as Turkey will have done by the time it joins the Union.

Enlargement has not diluted the stability and prosperity of current member states; it has enhanced it. It has peacefully united much of Europe after generations of division and conflict. It has increased the influence of the EU in the wider world.

So why Turkey and why start now? Estimates are that Turkey's economy will grow by 10 percent next year - more than any of the economies of the current European Union. Half of Turkey's trade is already with the EU, and it is already a major market for British and EU exporters.

The political case for Turkish accession is even more powerful. It would show how diversity of culture and religion is compatible with a unity of purpose. A stable, prosperous Turkey, a secular nation with a majority Muslim population, anchored in the European Union, would be a powerful symbol.

Why now? Because it's time. The prospect of EU membership, particularly over the last three years, has driven an impressive process of change in Turkey. Prime Minister Recep Tayyip Erdogan's AKP government has pursued a thoroughgoing and courageous program of reform, including the abolition of the death penalty and measures to combat torture.

Last December, the European Council decided that Turkey had sufficiently met the Copenhagen political criteria to begin negotiations on Oct. 3.

So what's the problem? In part, it is the still-unsettled issue of the divided island of Cyprus. In 1997, it was Britain that took the lead in arguing that the absence of a settlement should not be a barrier to Cyprus joining the EU, and we welcomed Cyprus into membership last year. Sadly, the UN-sponsored process to unite the island, supported by the EU, was not successful. But we continue to support UN efforts.

There is still a lot of detailed work to be done before Oct. 3, but with good will it can be. Yet it is clearly right that the European Union should now follow through on its decision to begin negotiations under tight European Commission supervision. To do otherwise would not only compromise the credibility of the EU but might also endanger the considerable progress already made in Turkey.

We should be very clear about the danger that represents. If we get it wrong now we could find that we have a crisis on our own doorstep.