You could get one of these.
I don’t know if they exist for UK style or if it’s only for Europlug.
But it should be fairly easy to buy a Europlug to USB.
But these has been banned for a very long time here.
The reason they got banned are probably not much of an issue today, it was because people overloaded the wires.
A LED bulb and a camera will not overload the wires.
But if they are banned in UK also then I would believe you make your insurance invalid whatever happens.
How big is the enclosure? UK Wiring Regs allow you to spur a standard socket-outlet from a lighting circuit in specific low-power cases. So if you have a friendly electrician, or are competent yourself and if there is room, you could fit a socket-outlet in the enclosure and plug in the mains adapter for the camera.