I was only in Scotland (skipped the London & south of England part to see more of Scotland), but Edinburgh was great. Went to the Willow Tea Room in Glasgow for my daughter's 21st birthday.
Charles Rennie Mackintosh The Willow Tea Rooms, Glasgow.
Of course, I'm sure you can find fun things to do around London (post in the main OT&B section, and I bet you can get a lot of international suggestions)
