As I said, I've never tried.
However, the aperture in the one pictured above extends almost as far as the hoes for the faceplate screws, which makes it about a 50mm square - and, having just tried, I can confirm that I can get most 13A plugs through a hole that size in a piece of cardboard! That' assuming, of course, that there is nothing behind the aperture which reduces its effective size!!
Given that one can(I presume) 'hook' the earth pin over the edge of the aperture, one only has to get the L&N pins 'through' and they (plus 'case') are rarely more than 40mm or so.
Kind Regards, John