Thanks to Terry Clark we can be sure this is not Oakington but is Abingdon. Gnat XP536 / 103 is from the CFS at Little Rissington. XP536 was tragically lost in a collision at Valley in the mid 1970s.
photo from Barry Davidson, dated 1968 the Piston Provost XF877 is apparently a visitor from Shawbury. The tower in the background is the original watch office.