In message , at 12:25:22 on Sat, 28 Mar
2015, tim..... remarked:
An hour from London:

though not within "discount" day return distance :-(

What's that?

which bit don't you understand?

They are not at locations at which it is possible to walk up to the
ticket office and get cheap return ticket for immediate travel

You either have to plan ahead and buy "advanced" tickets or suffer the
extortionate walk up fare

A Cheap Day Return *is* a walk-up fare. And not hugely cheaper.

Take Whittlesford Parkway, for Duxford Air Museum: £21.10 versus £25.20
for the period return.

There's a cheaper Super-off-peak day return at £16.40, but as you can't
leave Liverpool St before noon it has limited application for the OP's
purposes.
--
Roland Perry