London Tour Guide for a day?

Hello. My husband and I are in our 60's. We have been to London in May, 2009 and May, 2010. We will be there agin this September. We used Gray Line public tours. They are based here in the U.S. We have made reservations with that tour company in Paris, London, Canada, Washington, D.C., Boston, New York, Bruges, Italy, Paris, Switzerland, etc. They do day tours and are wonderful. We have taken the general tour of London, Stonhenge, Windsor, Bath etc. They have numerous bus tours to pick from. They picked us up right across from our hotel (Crowne Plaza Kensington, 100 Cromwell SW7 ER4) or we met the tour at Victoria Station. You can look at the choice of tours on-line at Gray Line.com. Elaine Obermann [email protected]