Trying to locate a fire alarm head and being in a rush I stupidly forgot to take a picture. I know its a long shot but I'll try and describe it. Its not like the Apollo type heads where they twist on and off, this is a more bulbous or round type of design, cream or white coloured with the smoke vents round the detector half way up. It also plugs on and off the base without any twisting. I would say about 10 years old. Just the analogue type. Edit, a bit like this but with the vents higher up, its a bi-wire system as well I think.
No its for a proper fire alarm panel. I've seen them several times before and just last year I removed a full faulty system from a house someone had just bought and fitted new. This is a grainy picture from rightmove showing the old head on the ceiling.
Mystery solved. https://www.firetradesupplies.com/collections/fike-twinflex-devices/fike-twinflex-devices