Don't do London without a good map, and mind that the bloody Tube closes at 1830 on Sundays. And don't expect tourist information to be open at the times you need. Most cities are pretty nice, and compared to the rest of Europe, the chances of getting your money (and passport) nicked in broad daylight seem pretty slim. Still, stuff your ID down your underwear in places like Manchester, London, or other big cities. Don't got into London's Victoria Coach station if you like to avoid junkies, hotel tauts, luggage thieves, and pickpockets. Rest of the station seemed pretty ok, just don't go near the coach bit.
White cliffs look nice, especially so from the sea. Not sure if there are tour boats, but the view from a boat heading for Dover is always better then the view from Dover looking at the boats. Though, if you happen to have a really clear night, you can see France quite clearly from Dover's cliffs.
How long are you staying? Are you looking for nature or urban stuff? Historic? Roman? Stoneage? How will you be travelling around? (If you've got the money, take trains. The comfort of a train over a coach is worth it. National Express is quite reasonable, but coaches do tend to get really annoying after an hour or ten.)
Pounds are expensive, so everything is just one and a half times more expensive then in the rest of Europe. Food isn't all that bad, if you stick to pubs, don't eat fast food except for fish and chips or kebabs. Drink is hellishly priced due to taxes. Traffic comes from the other side of the road.
