Live cable in wall

Looks like the mains cable leaves that hole going upwards? Presumably there isn't a light switch, or mains socket aligned with it? If not then it isn't within a safe zone, and it doesn't look like it can be more than 50mm from the surface of that Paramount Board.

Yes, it does go upwards to a pull switch on the ceiling.

The 'headboard' of the bed was a 7ft wide x 5ft tall sheet of wood fastened to the wall and this was behind it when we took it off.

And there's the answer isn't it? Staring me in the face all the time - just disconnect at the pull switch!

I've had a long hard day today and what is obvious now wasn't before, so cheers Andy, thanks lol

I assume it's not a double-pole pull switch, so the question is whether it's the live or neutral which is switched. If it's the live, fine, just disconnect it. If it's the neutral, then disconnecting it will leave the rest of the wiring to the junction box and led power supply live unless you disconnect the live wire too.

Many years ago after we moved in I found an apparently blank cover plate in the lounge. On it was a paper label stating "circuit is disconnected". When I examined it I found it wasn't a blank, but the label was covering an old round 3-pin lighting socket. I took it off and checked the wiring to the socket. It was live!

looks like a cable was dropped down from the loft? might be worth going into the loft and see if a T&E cable comes out into the loft above the wall? you will probably find it will trace back to a room ceiling lighting rose....