We just returned from London and I wanted to recommend two tour guides we used as there are so many to choose from and we were so happy with both of these gentlemen.
1) Johnny from Stonehenge Travel ([email protected]) - There are several options available but we did the early morning private tour of Stonehenge (left London at 4:30 AM) followed by breakfast in Salisbury and then a self-guided tour of Windsor Castle (back in London at 2:30 PM). Yes, it's early but worth the early rise/cost as we were part of a very, very small group at Stonehenge. Johnny provided history of the area throughout the day--well worth the cost.
2) Gavin Webb (www.tourguideoflondon.com) who we used for The British Museum. He brought the exhibits to life, helped maneuver us around crowds, pointed out interesting exhibits we absolutely would have walked past without understanding the significance if we were alone. My teenagers really enjoyed the morning with Gavin. He is a Professional Blue Badge Tour Guide.