Turkey's constitutional court opens a case today that will have momentous, and possibly disastrous, consequences not only for Turkey but also for much of the Muslim world (see page 34). It is a case that could end Turkish hopes of joining the European Union for ever and transform one of the West's most vibrant strategic allies into a feuding and embittered society, torn between military repression and Islamic fervour.

For what the court is attempting to decide is whether Islam is compatible with secular democracy. If it rules that the present Islamist Government has undermined Atatürk's constitution, it will declare the entire ruling Justice and Development (AK) Party illegal and order the dissolution of one of Turkey's most popular and successful governments. If that should happen, Islamist parties throughout the Muslim world may turn their backs on democracy, arguing that, since secularists will never accept them, they should ignore the democratic process and seize power.

Few court cases have been more political or less justified. When the chief prosecutor opens proceedings today with the accusation that Recep Tayyip Erdogan, the Prime Minister, is seeking to transform Turkey into an Islamic state, most Turks will hear the voice of the powerful and resentful armed forces. The Army, which sees itself as the guardian of secularism, has never accepted either Mr Erdogan or his party. Four times in the past 50 years it has staged a coup, coming close last year to doing so again over the the Prime Minister's proposal to name a prominent Islamist as the next president. The wily Mr Erdogan, however, called a snap election, came back with an increased majority, installed Abdullah Gül as President and implicitly challenged the military to defy popular opinion and overthrow him.

Having failed in their public warnings to stop AK returning to power, the generals have thrown their weight behind this latest coup by stealth. Counting on the secularist constitutional court to accept the legal challenge by the opposition, they now hope to prove their contention that recent government decisions, especially the attempt to lift the ban on headscarves at universities, were indicative of an Islamic agenda.

The prosecution - and the generals - are seeking a five-year ban on politics on 71 party members, including Mr Erdogan and President Gül. The uncertainty is already damaging markets and inhibiting foreign investment. The European Union has taken a strong stand against the trial, saying that accusations against the Government should be debated in parliament and that it is up to voters, not to a tribunal, to decide whether the AK Party, which now proclaims itself a “conservative democratic” rather than Islamist party, is fit to hold office.

If the Government is dissolved forcibly by a court decision, the EU would almost certainly break off accession talks. This would please the military Establishment, which has become increasingly nationalist and views the EU with suspicion, especially in light of EU condemnation of its campaign against Kurdish rights and the suppression of writers considered unpatriotic. This is just one issue where the secular Establishment has forfeited the former warm support of the West, while the AK Party has impressed outsiders by a swath of reforms and progress on human rights.

Muslim governments are watching Turkey intently. Most are fearful that attempts to draw Islamist parties, hovering on the edge of legality, into the political framework will founder if AK is banned. That would radicalise Islamists, revive conflict with the West, thwart political reconciliation across the Muslim world and lead to lasting bitterness. A lot rides on this week's court case.