Fire rated downlights have the capacity to improve safety by restricting the spread of any fire that may occur in the property through the ceiling in which they are fitted therefore they are often the fitting of choice for any application. Fire hoods are generally a nuisance to fit and whilst they do provide the required fire rating you can probably buy new fire rated downlights for less than the price of a fire hood.
The fire rating of any fire compartment must be maintained and this can be done by the use of fire rated downlights.
However it is fairly uncommon to have downlights in a fire compartment ceiling, probably the most common situation would be in blocks of flats where the ceiling of one flat is the floor of the separate fire compartment of the flat above, in a situation like this then fire rated downlights would be mandatory (if you have to fit downlights).
For the more usual situation of fitting downlights in a property where the room above is part of the same fire compartment (i.e a normal domestic residence) then the ceiling is not a fire compartment and so does not have to have fire rated downlights. However since they are often similar prices now it would only be in limited access situations that I would consider non fire rated, and also some LED downlights now come in fairly flat fire rated versions avoiding the problem. A standard plasterboard ceiling on normal joists is unaffected by the penetration of downlights so the fire rating (as opposed to the compartmentalisation by fire separating elements) of the ceiling would be unchanged no matter the type used. You would still be complying with the requirements to maintain fire resistant materials.
