Dave Arquati wrote to uk.transport.london on Tue, 11 Jan 2005:

Thinking about it, it would be quite hard to abuse the system anyway - I
imagine the number of return trips where one leg is by Tube and the
other leg is by bus are small - except perhaps for when the return
journey is after the Tube stops.

Oh, I quite often do that when going into London - if I'm in a hurry, or
have a fixed appointment, I'll take the Tube there, and if I'm tired
after shopping I'll probably catch a bus home. Or vice versa.....
--
"Mrs Redboots"
http://www.amsmyth.demon.co.uk/
Website updated 2 January 2005