On 30/08/2016 00:29, John Rumm wrote:

You can get thin plastic finger protector plates designed to go behind
sockets and switches - they create a 1" (ish) wide boarder round the
back edge of the faceplate that stops the wall getting finger prints all
over it. Also handy for hiding gaps.

e.g: http://www.amazon.co.uk/dp/B004GU8J3A

The idea of even more plastic isn't really doing it for me.
I suppose I might be able to chop up some spare back boxes to make some
sort of extension to extend the box to the face of the plasterboard
thereby enabling a better chance of successful filling...

Cheers
Pete