There are building regulations covering the intumescant or other methods to reduce and prevent fire risk. However this is more to do with the design of the building than the down lighters and in one kitchen you may need no special system and in another kitchen you may need special hoods etc.
The electrical regulations stipulate a 100mm clearance to combustible materials but do not allow for different types of light producing different heat and just say you should follow manufacturers recommendations. So a lamp which says suitable for mounting on combustible materials can be used.
I do question the word down lighter as there are so many lights which shine down and are also in-bedded in the ceiling.
The whole idea of shining down is a problem as floors do not reflect light very well using spot lights which can be angled to light up special areas are good but you will need general lighting as well. The small 50mm fixed lamps are not really much good at lighting.
I think your post does not make it plain to if you are asking if you have to have down lighters or if those down lighters have to be coated with the special material. I would have thought you were asking about the heat resisting material?
Using small 50mm down lighters in suspended ceilings where there is free air above them I have not found a problem but when one starts to use hoods and the like I have found the lamp holders fail due to heat. So I would say if building regulations for your type of ceiling requires hoods then don't use that type of lamp.