[Paul Corfield]
A photocard *is needed* to buy or use :-

a) monthly or longer period Travelcards that include validity to a
National Rail station beyond Zones 1-6
b) monthly or longer period Tube only point to point season tickets
(between stations in Zones A-D) issued before 2/1/07 until expiry of
ticket.
c) 7 day, monthly or longer period National Rail only season
ticket.

[Bob Wood]
But neither b) nor c) would be valid at Liverpool Street Underground, so
the OP would hardly have been talking about either of them.

True, but I have still found it interesting.
--
Michael Hoffman