On Saturday, July 5, 2014 11:38:20 PM UTC+1, Stephen wrote:
Are there any better solutions than digging out the new metal back box,
fitting new box and redoing plaster around the replacement box?

Fix it with one screw and hold the other screw in with blutack to be cosmetic.

Then remember not to use that socket in case it's wobbly.

Of course if you're a professional electrician working in someone else's kitchen you can superglue the socket to the plaster.

Owain