Thank you again. Whenever I go to London I use a One Day Travelcard

Get an Oyster. If you happen to make fewer journeys than the price of
a ODT, you save. If you make more, it's capped anyway. It spares you
having to decide in advance which zones you want, and you don't need
to queue to get it.

The things where a travelcard is bundled into a day return (which
Chiltern have done for a while, but Virgin now seem to do as well) are
marginal: they're six zone, which is good if you're going to use it
but less good value if you aren't. And I'm never entirely sure
(perhaps someone could comment) on if they include buses.

ian