Dave Arquati wrote to uk.transport.london on Tue, 21 Sep 2004:

I never realised that for a bus commuter travelling twice a day for the
five working days, Pre-Pay (in both 2004 & 2005) is cheaper than a Bus
Pass!

If, and only if, you only need to use one bus to complete your journey.
For me, going to Streatham several times a week, it always needs two
buses or a longer walk than I've often time for - so I buy a bus pass
(which may not be cost-effective, but is simple!).
--
"Mrs Redboots"
http://www.amsmyth.demon.co.uk/
Website updated 11 September 2004