There is not much that you can be absolutely certain on, especially in politics.
But I would almost be tempted to bet the house that Geert Wilders will arrive in the UK and be allowed to leave the airport unmolested.
Just about the only thing that we can be certain of, is that when the EU makes a law, The UK Government will never, ever, act in contradiction to it. Free movement of citizens within the EU is one of their crowning diktats. There is no way, at all the UK Government will be standing in Geert Wilders way tomorrow.
UK laws, they have no problem ignoring. EU ones are a different matter.
Update: 12-Feb-09: I stand corrected. Today is a very bad day for free speech in the UK