Fly Air Wales, there is nothing between the pilot and the passengers apart from the stewardess.
Fly Air Aran and watch the pilot say hey fatty wait for the next flight.:D

I've just asked the daughter and she says if there was a door it was constantly open because she sat fascinated looking at the pilot and the instrument panels.

It could be the curtain was to allow a little privacy especially during a night flight with regard to passenger compartmjent lighting.

Either way I'd have expected the door to be closed and locked, even on an internal commercial flight.