Andy Dingley wrote:

Mounting at 45° is even better. It looks like they're meant to be this
way and "vertical", but it avoids the cables getting in the way. I've
not seen "domestic" box mounting sockets for this but it's common
enough in the "equipment racking" world.

Just what I was thinking. For a DIY 1-off it wouldn't be too time
consuming to buy a couple of MK 734s or 735s and mount them on your own
metal front plate. That would give you a 2-gang unswitched socket.
Switching, if required, could be provided using separate switches, e.g.
a 2-gang 20 A DP switch assy made up from gridswitch parts.

--
Andy