I don't think it has to do with having been in the UK on wifi, but my computer does that when I've been at several hotels with wifi sometimes (especially this one hotel we stay at when visiting my brother! So annoying!) You may need to go into your Network settings (Networks and Sharing Center on Win Vista) and clear out any of the other networks listed when you click on "Manage Wireless Networks". You should see the names of different networks you used while on your trip. You may also have to reset your wireless router (unplug, count to 10, then plug in again and wait for it to load, then try connecting again.) If worse comes to worse, you might have to redo your wireless network. I had to do this last week when we had a lightning storm and it wouldn't connect anymore (though it saw it on the list). I had to call the router people and they helped me undo the settings and then redo it and change wireless channels and stuff....
And I know this sounds basic, but have you tried shutting down your computer and rebooting completely?
Good luck!