State visits are an opportunity to strengthen Britain's overseas links, renew friendships, deepen political co-operation and send a symbolic message to public opinion, at home and abroad, that the host country matters. Few visits have been as timely or as significant as the Queen's current tour of Turkey. As she noted in her banquet speech, the country is uniquely positioned as a bridge between East and West at a crucial time for the European Union and the wider world. It plays a key role in promoting peace, stability and development in an unsettled area. And it has remained a staunch Nato ally throughout the Cold War and during decades of Middle East turmoil.

For Turkey, Britain is equally crucial. This country has been one of the most consistent champions of Turkish entry into the European Union. It was Tony Blair who began formal entry negotiations during the British presidency, and the Government has pushed hard to stop its EU partners backsliding on this commitment. The long-shared history, which includes the Crimean War as well as the disastrous Gallipoli campaign, has forged a mutual respect that still lingers in public consciousness, so that Britain enjoys warmer relations with Ankara even than Germany, with its large Turkish population.

More than sentiment, however, lies beneath Turkey's strategic importance today. Stability in Iraq depends very largely on restraint in Ankara. Turkey refused to join in the attack on Saddam, but the vicious campaign by PKK separatists made it especially sensitive to the emergence of a separate Kurdish entity in northern Iraq. But, despite military incursions in hot pursuit of terrorists, Turkey has played a responsible role in promoting unity and stability within Iraq. That restraint is all the more important as Iraq begins to emerge from post-Saddam turmoil and violence.

Almost more important than what Turkey does, however, is the example of what it is: a Muslim, secular democracy, a regional industrial power and a society that remains free and open despite the pressures of religious extremism, prickly military nationalism and Westernised culture often at odds with conservative rural traditions. Freedom of expression still has some way to go: the attacks on the writer Orhan Pamuk have been demeaning. But what makes Turkey uniquely important today is its attempt to reconcile moderate Islamism with democracy and economic development. For the first time in decades, Arab countries are following developments with close attention. For if the Government of Recep Tayyip Erdogan, despite a good economic record and pro-European orientation, is overthrown - directly by a suspicious military Establishment or through a legal device on the grounds that it is undermining the secularism - Islamists elsewhere will conclude that there is no point in moderation, as democracy will never accept them or let them to come to power legally.

The West therefore has a vital interest in the survival of Turkey's elected Government, not only because of its competence but because of its global example. Friends are better placed to say so than critics; the message given by the Queen and the Foreign Secretary is one that should be heeded by the Turkish generals and Islamist campaigners alike. The Ottoman Empire once influenced the entire Muslim world; what happens in Turkey still matters far beyond its shores.