As a general rule, if there is a habitable room above, then fire rated are required in the room below to maintain the 30 minute fire protection and acoustic properties of the ceiling.
Non fire rated are very cheap you can get 10 for about £30 inc lamps, compared to about £50 or £60 for fire rated. People who install crap and cheap have no knowledge of building regs, i.e DIY charlie, they just want cheap and looking nice, and those who sell them just want money and couldn't give a ----.
I personally would ban non fire rated downlights, they are crap and dangerous, for a couple of quid extra each you can get the proper thing.
Cheers........Howard