I remember the TV serial and have the DVD (must play this some time) but the book is much better.
Set in a London which exists under its streets, this is a highly imaginative adventure story whose hero
finds himself in this alternative world because of a small act of kindness. The use of existing (or
rather, above ground names) is skilfully used - as well as the obvious possible such as 'Knights' Bridge' and 'Earl's Court', there is the Angel of Islington and clever use of disused Underground
Stations like Down Street and the British Museum. Obviously, the reader needs to suspend disbelief to enjoy the story but it is an exciting adventure tale in its own right with the locational disruptions of
one's knowledge addigint to the excitement. Very good indeed.