Turkey's date with destiny, October 3 - the same day, coincidentally, that Germany was reunited in 1990 - was set last year when the then 15-member EU was finalising its historic 10-country enlargement.

It has been a very long time coming: Turkey has been a stalwart member of Nato since 1952 and was first recognised as a potential member of the European club as long ago as 1963, only a few years after the creation of the EEC. Britain is a keen advocate of its EU membership, as is the US. Both see the secular Muslim democracy as a key regional ally, a beacon for Islamic and Arab countries and proof that a "clash of civilisations" with the west is not inevitable.

But mounting anti-Turkish feeling in several European countries and last summer's shock rejections of the new EU constitution in France and the Netherlands - part of a wider political and economic malaise - have created grave doubts. Hence this week's alarm call by Jack Straw, Britain's foreign secretary, who is now in the hot seat of the EU's rotating presidency, that it is vital to stick to the October 3 start date even if, as is widely expected, the actual negotiations drag on for many years.

The immediate problem is the vexed question of Cyprus, one of last May's new entrants. The hope had been that a long-standing UN drive to reunite the divided island would bear fruit before it joined. But since it did not (though more because of the Greek than the Turkish side) and because Ankara is refusing to recognise the Nicosia government (which for the EU legally represents the entire country), the launch of accession talks is in jeopardy.

Recognition is extremely difficult because without a comprehensive peace settlement it would undermine Turkey's own 30-year military presence and the breakaway Turkish Republic of Northern Cyprus. But by flaunting its position at this highly delicate moment, Turkey has given ammunition to its enemies.

Chief amongst these is France, where polls show much of the anti-Turkish prejudice expressed by the former president and author of the constitution, Valery Giscard d'Estaing, whose circumlocutions about "cultural differences" are only slightly less offensive than the cruder view of another clever Frenchman, Voltaire: the 18th-century thinker called the Turks "a reminder to Christians to atone for their sins".

But there is an even bigger obstacle looming in Germany - assuming Angela Merkel's centre-right CDU wins this month's election: Ms Merkel wants Turkey - which supplied so many of the gastarbeiter who created the German economic miracle of the 1960s - to be offered only a "privileged partnership", not the full membership that has awaited all other candidates, from Estonia to Bulgaria, at the end of their negotiations.

Another key opponent is Austria, where it sometimes seems that Ottoman janissaries are still besieging Vienna as they did back in the 17th century. Its chancellor, Wolfgang Schussel, also favours a halfway house and "open-ended" negotiations for the Turks.

The problem is that offering something different only for Turkey would appear to prove the resentful charge that the EU is a "Christian club" and risk a dangerous anti-European, and perhaps fundamentalist, backlash. Recep Tayyip Erdogan, the Turkish prime minister, has warned that he will "walk away for good" if the talks do not go ahead on schedule.

If they do start on time, it will be a very big deal indeed: no country that has begun negotiations on joining the EU has failed eventually to make the grade.

Although actual membership could be 10 or 15 years away, by then there will be more than 80 million Turks, probably outnumbering Germans. And with voting power tied to population size, Ankara will be as important a player as Berlin, Paris and London - a key reason for the mounting opposition. Another is the fear of large numbers of poor Turkish migrant workers flooding western European labour markets, though restrictions could be imposed for a transition period.

Turkey and its supporters are understandably worried, though they have a strong case when they argue that the magnet of EU membership has already generated huge advances under Mr Erdogan's conservative, moderate Islamist government.

The country's old Midnight Express image has faded and torture has been banned. There are now Kurdish language broadcasts, and the grip of the powerful military, keepers of the Ataturk flame, has been weakened. The economy is in good shape after years of crisis and inflation under the generals. It is an increasingly attractive market for foreign investment.

Not everything is perfect. Implementation of some new laws has been patchy, and some worry about minority rights. Until recently there was greater openness on the ever-neuralgic question of the Armenian genocide of the first world war. That, however, has faded, and there is now embarrassment about the case of the internationally renowned novelist Orhan Pamuk, facing charges of "belittling Turkishness" over his brave comments about that dark period.

Hectic diplomacy is likely across Europe over the coming days, perhaps going down to the wire on the eve of October 3. There will be brinkmanship and haggling over the precise terms of the negotiations,and attempts to square the circle of Ankara's non-recognition of Cyprus. Obscure and complex it may all be, but the stakes are very high. As Abdullah Gul, the Turkish foreign minister, put it: "The last 100 metres of the marathon should be run very carefully."