There's been a lot of discussion about Potter in the UK park in this thread. Some excellent points on both sides so I won't try and restate them all, but worth going back through the thread and having a read if you're interested in it.
The shortest summary possible is that it currently doesn't look like there will be any Potter in the park at opening at least (for many reasons) but nothing is off the table entirely this early in the process, so no one can say for sure.
But as I say, if you're interested in reading everyone's ideas about why it will/won't/must/shouldn't/could have a place in the UK park, you'll enjoy going back through the thread to find the various times it has been discussed.