Michael,
It's gonna be a bloodbath. They're expecting 30,000 English fans. The only bright spot is that the Turks didn't qualify but there is going to be loads of trouble, whatever the police do - you think that the English hoolies haven't been organising for this since Germany got the gig?
The British and German polices work together, they´ll use the possibility to restrict the freedom to travel, Germany will do border controls (which we usually don´t do to Schengen countries), and the Brits will prevent their hooligans from leaving the island. In the worst case, we can use the military, but it probably won´t be that bad.