@ Richard ~ do they have regular running and "steam in the shed" sort of days? I am thinking out loud that combining a visit with seeking out the Red Kites in the Chinnor area (there is a nature reserve whose name escapes for now?) might make a good SE PoTN meet???
What they do is a little limited, http://www.chinnorrailway.co.uk/timetable it is only a small railway not on the scale of Midhants, they run steam most Sundays in the summer months. They have good free car park and a little buffet on the platform which does good bacon buttes which is popular with walkers and cyclists.
They only have one station at Chinnor so once you are on the train you are on the train until you get back to Chinnor.
I go there as its localish easy for me to get to
Someone mention Red Kites, this was taken with my 24 -105 is quite a heavy crop