Val & I know nothing about visiting London. We are talking to folks who have done the London-Paris ABD adventure and anybody else with actual London experience. QUOTE]
You are thinking of doing this pre-cruise, right Jeff? That's what I would recommend, because London is very busy and sightseeing intense so it would be nice to have the relaxing cruise after it. That being said, we can't add on pre-trip (we'd miss my daughter's birthday) but I am still toying with the post-cruise extension in the English countryside.
As far as what to see in London, I was very impressed by the British Museum. There are lots of daily free tours giving an overview or focusing on one small area. Also, I listened to this podcast and it was great:
http://www.britishmuseum.org/explore/a_history_of_the_world.aspx
The Tower of London and Westminster Abbey are must sees. I could have spent a week in the Abbey alone. Buckingham Palace will be closed in October (it's only open to the public when the queen is on holiday) but you can visit the Royal Mews (stables) where the carriages are. Brian and I visited Windsor Palace which is just outside of London. It actually has a much more extensive history as a royal home than Buckingham. It is the largest and oldest inhabited castle in the world. They have their own changing of the guard, which is much less crowded than the one at Buckingham. St. George's Chapel on the ground is the home of the Order of the Garter and the burial site for most of the recent British monarchs plus Henry VIII, Charles I, and George III and others (I am a British history nut in case you couldn't tell.)
Here's the website for the royal palaces:
http://www.royalcollection.org.uk/
Harrods was lots of fun and although I am terrified of heights, I really enjoyed the London Eye. St. Paul's Cathedral has gorgeous acoustics and regular, free organ concerts. Brian and I went to a short 45 minute one and it was very impressive. The theater district is fun with lots of restaurant options.
Laurie