Timothy Murphy pretended :
I have a round plastic ceiling rose in our kitchen
which I am unable to rotate in order to remove it.
I guess the heat from the bulb below may have distorted it,
or just made it adhere tightly to the part attached to the ceiling.

I've tried turning it with a (not very good) plumber's wrench,
after applying WD50 liberally, but this just slipped round.

I thought of drilling two holes in the flat bottom,
inserting screws and using a screwdriver or similar to turn it.
Any better suggestions?

Have you one of those rubberised engine oil filter removers? Like
rubber strap, with a handle - the more you try to turn the tighter they
grip, about a pound in a pound shop.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk