Well I found them. This egress casement hinge fit the bill perfectly. After poking around for long enough I discovered an "egress" casement window hinge (egress means for windows that can be used as exits in emergencies). While the hinge in the picture on the website is open to a bare 90º, I bit the bullet anyways because the track gave it more space to turn....
Yes, they are called “rising butt hinges”.
The “joint” is at an angle and as they rotate it gives vertical movement.
Here is a link to one such product: https://www.amazon.co.uk/Rising-Butt-Door-Hinges-Stainless/dp/B00GK5QLY8
You can get various conversion patresses which will fit over a flush 1-gang box and present a surface 2-gang box, eg
and conversion sockets, eg
If you want to fit a single socket on a double box you'd probably need to use a Euro module faceplate, Euro module socket and blanking plates
If you just need a decorative cover then 'finger plates' are available ...