On 5 Dec, 13:27, Matthew Dickinson
wrote:
It's not available from the automatic machines, but the ticket seller
is able to issue it as a One Day Travelcard, as long as they set the
origin station to Amersham.

Is a Zone D travelcard actually an 'all-zones' travelcard - i.e.
freedom to roam within zones A to D as well as in zones 1-6? Or a
return to BZ6 with freedom to road just within Z1-6?

Because I can see problems with this suggestion if it's the latter....