Thank you all. The property dates back to around 1973 and I think this will be part of the original installation. Oh, and its plastic, by the way, and does look like a batten holder.
I love the quirky, good humoured way you ask for a pic, BAS; to follow when I dismantle said fitting again.
An additional query, if you would be so kind.
I've also taken down an old ceiling fan/ light combo to replace it with a three bulb metal light fitting. When I took the fan down I found three cables emerging from the ceiling. Two neutrals from the circuit cables were connected to one block and thence to the neutral terminal on the fan, the third neutral from the switch cable was marked with red tape and connected to the switch terminal on the fan. The earth wires from the circuit and switch cables plus the earth wire from the fan were joined together in one plastic connecting block and the three lives from the circuit and switch cables were unused, terminated in another block and taped up.
After I disconnected the fan, I connected the two neutrals from the circuit cables to the neutral from the fitting, connected the red taped neutral from the switch cable via another block to the live from the fitting and connected the earths from the circuit and switch cables to the earth from the fitting. I've left the three lives wires from the circuit and switch cables taped together unused whilst I seek guidance on here. Until I connected the wires as described above none of the other lights on the circuit would work, but I haven't switched the new fitting on yet.
Is it safe to flick the switch?