That was unexpected, I thought my solution was a workaround. Hopefully you are having less problems now.
After I ordered several single socket dual dimmers to find one that could support two C202N modules side by side I found one. It is the "Power Pro Double Dimmer Switch 1 Way Turn On/Off."
I beleive it is also sold by B&Q in the UK although this is a 2 way so it isn't quite the same model but more importantly, the face plate looks the same i.e., the rotary buttons are spaced further apart than most others:
