Donald Tusk returned from Turkey bearing an unhelpful message. Yes, Turkey would stem the tsunami of migrants heading for Europe, but at the cost of two things; we must abandon all support for the Kurds both in Iraq / Syria and among the 20% of Turkey's population, and we must ratchet up Turkish rights of free movement in Europe. The cost of our support for Kurdish independence is free passage through Turkey of 1m migrants a year or more.
Sunni Moslem Turkey will also oppose any moves to leave Shia populations with greater power in the region. As a NATO member, Turkey usefully disguises self-interest behind the pretence of a NATO border; in terms of real-politik, Iran may now be a strategically more superior partner for Europe than Turkey, and a European alliance with Russia to leave a Ba'athist rump in Syria intact and to destroy Sunni insurgents in Syria and Iraq, an act that furthers the establishment of a Kurdish state, with both strands clearly contrary to Turkish interests, offers us far more, including turning off the tap of war in Syria that feeds the flood.
And naturally, it is in Turkey's interest to keep the war in Syria going for as long as possible.
So if Calamity Dave and his daft chums are minded to invade somewhere as a sign of action, he'd do better to co-ordinate the destruction of Turkish military capability than anything else; if we intervene in Syria, we're fighting enemies covertly supported anf supplied by both Turkey and Saudi Arabia, unless Calamity Dave does exactly what the Turks want - to turn on Assad and the Christians, wiping them out and creating a Sunni hegemony from the Med to the Caspian.