Great photos of this fantastic old map, discovered in place (presumably during the Bakerloo/Northern Line station refurbishment works) and now protected in situ by some rather ugly chicken wire. Note that the loop at the western end of the Piccadilly Line to Heathrow Terminal 4 is still under construction, which had been completed by the time this version of the map (May 2013, 3 stars) came out in 1988.

Source: jaggers/Flickr – links no longer active