In message , at 21:28:41 on Wed, 19
Apr 2006, Andy remarked:
The longest Tube journey is on the Central Line, West Ruislip to
Epping, at 54.9 km (34.1 miles).

Can't you do Cockfosters - Cockfosters via the Heathrow loop that would be
longer?

Not at the moment, the loop is closed.
--
Roland Perry