<Monty Python> I confess! </Monty Python>
Doing Tube Relief served merely to whet my appetite (though perhaps we should've been more proactive in our promotion of the cause ion the day) for doing "it" for real, as it were.
Staying in Beaconsfield Old Town (that's the bit up by the A40), rather than Amersham, the night before was definitely worthwhile (and cheaper, even taking into account the £10 cab fare, as the room was £39.95 for the night and we got three people in there).
Now I just need to work out a route to link London Bridge and Chiswick Park, via everywhere else, in the necessary amount of time for the finish
Cheers,
Barry