I spent a couple months over in the UK in the early 90s, and the best advise I can give you is to get a British Rail gold pass. If I recall correctly, it's good on all the trains and even metro lines in most big cities.
My favorite spots were Edinbrough (especially the royal mile), Loch Ness (which is actually Inverness, Scotland), and anywhere in London.
Scotland is more of a casual atmosphere, whereas in London, certain places will or will not let you in based on your clothes(!?).
Avoid tour busses. Very boring, and you might as well sit in your hotel room and look at post cards.
If you like beer, like I do, hit as many pubs as possible and absorb the local color. You will meet some very nice and fun people.
Wherever you decide to go, have fun and good luck!
