Thanks again Spark123, that's really helpful - I will have a look and see. I was struggling to get the bezel off by pulling (not too hard as I don't want to damage it) so will try and unscrew.
Wow Spark123, very many thanks for the swift response!
That sounds good, thanks for the Screwfix link. Do you know if I can gain access to replace it from below (via the hole in the ceiling that the light/fan comes through)? as I cannot access the kit from above. I think its a Manrose 100mm kit...