You will need to call Disney on 001 407 934 7639. The lines open at 7am EST, so you can call from 12 noon from the UK. I don't think there's any word yet of precisely what day they go on sale, but keep an eye on the boards for that news.
If you get a Cast Member who tells you they can't ship the tickets to the UK, you will need to persevere. Some of them are more informed than others. Tell them you've done it before, or know someone who has done it before, and they will usually go away and check. If all else fails, just call back until you get someone who knows!