Mizter T wrote:

See this from the FAQ section of the Young Person Railcard website -
the last sentence in particular...
(I've copied it in full for posterity should they ever correct it)

-----
14. Can I use my Railcard for tickets for travel on the London
Underground? All discounted rail tickets bought using your Railcard
routed 'between London termini' are valid for cross-London transfer on
the London Underground. Off-Peak Day Travelcards (All Zones only) are
also available, subject to a minimum fare. Please note, however, that
you cannot use your Railcard to obtain a discount when purchasing
tickets from a London Underground booking office.
-----

Does this also mean I can't get a YPR discount on an Amersham to Aylesbury
ticket (a journey I'm due to make several times).

(Indeed what's the cheapest way to get a good discount on an extension from
a 1-6 travelcard to Aylesbury? PAYG to Amersham, then buy a return ticket at
the office there and on the way back jump onto the platform to touch in then
back onto the train, or a straightforward extension from Marylebone/Harrow?)