Update September 2010: I was able to visit another section of these tunnels beyond a bricked up doorway, under different ownership from the main tunnels. These tunnels are used as storage, and are pictured below (after picture 9).
Both sets of tunnels are privately owned, many thanks to the owners for allowing access.
Plan of the tunnels
The following tunnels are separated from the previous tunnels by a brick partition, as they are owned by someone else, and are accessed by a different entrance.