Hi
I was doing a "simple" replacement of a standard switch with a dimmer, and encountered the same problem that the box was not deep enough. It was going to be awkward to excavate further, and after some searching found that Wickes sell a 1 gang module Product Code: 204736, which is a plastic frame with a square hole in the middle. I had to enlarge the hole, but it then fitted perfectly between the switch and the box, and made a very neat job of allowing me to fit the switch.
They also make a double version.
It worked for me, but YMMV.
I was doing a "simple" replacement of a standard switch with a dimmer, and encountered the same problem that the box was not deep enough. It was going to be awkward to excavate further, and after some searching found that Wickes sell a 1 gang module Product Code: 204736, which is a plastic frame with a square hole in the middle. I had to enlarge the hole, but it then fitted perfectly between the switch and the box, and made a very neat job of allowing me to fit the switch.
They also make a double version.
It worked for me, but YMMV.