Thanks very much for taking the time to reply. ATM, I'm not doing anything except scratching my head! The story so far is as follows: After a brief interlude of occasional delays between flipping the wall switch and the lights coming on, the ceiling lights in half my house packed up completely. Assuming that a wire had escaped from one of the terminals, I thought it would be a simple matter to reattach the escapee, and re-establish the dropped connection. Not so.
I hoped it would be obvious, by its proximity to a particular terminal, which of them the errant wire had escaped from. Sadly, I displaced the loose wire when I removed the top of the junction box.
Having never met 3 core & earth before, I am confused by the non-standard configuration, and I can't work out which terminal the wire escaped from. The idea of finding out by trial and error- attaching it to each in turn and seeing what happens- doesn't appeal, hence my plea for guidance.
Kind regards, Denise