Lem - it is to stop pax trying to pee in the cockpit - a well-known British trait. Either that or it is some BALPA industrial thing.
Not-so - type confusion there, old chap! E&E only opens underneath fuselage - or was that where that stewardess went.................?
Serious hat on now, LEM - depending on which serial no. it is, they came from all over the world with all sorts of different mods.