Thought I'd report back now they're working.
A pal came round to help and checked the voltage the same as me. Then asked if I'd checked the fuse.
Of course I have!
So he checked anyway, with his multimeter, and found it dead. (Even though it visually looked OK). I checked with my multimeter and found it OK??
Weird, but a new fuse sorted everything out.
Annoyed, would be an understatement.