Well apparently we're looking at the inside of a Boulton Paul Turret.
Which plane? Hard to tell, could be many.
The guns seem to be tilted up all the way and the elevation lever doesn't quite look like what I remember to have seen on Halifax Bombers converted to BP turrets, so I'd rather rule out that it's a Halifax.
In theory it could be a Ventura, a Lincoln, or even a Liberator, a Blackburn Roc or a Short C/G flying boat, but that'd be an odd quest...
My bet is that it's a Boulton Paul Defiant Mk.I, the parts seen in the upper left corner would match the canopy fairing and the elevation lever would fit, too.
Best regards - Mike