a few pence will buy you a frame which sits behind the switch and lifts it off the wall about 6 or 7 mm so any dimmer will fit into a shallow box. You will probably have to use longer screws and maybe re-thread the lugs in the box. I used to chop new boxes in until i found these. I know CEF stock them and they save a lot of hassle and don't look unsightly either.
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