The main reason that fire rated downlights exist is that they restore your ceilings original ability to prevent fire from spreading. When you cut a hole into your ceiling to fit a recessed downlight, your reducing its ability to prevent or delay the spread of fire.
Fires can spread through the holes and once they've reached the ceilings main structure which is usually timber, it doesn't take long for it to to spread through the entire building.
A fire rated downlight seals off the hole and restores the ceilings fire integrity. Fire hoods can also be used to fire fire protection. Part B of the Building Regulations relates to this subject.
Our number 1 rule about fire rated downlights is: If in doubt, fit fire rated downlights. All of our fire rated downlights can be located here.
Most downlights are fire rated as standard, especially integrated LED downlights. Some non fire rated downlights actually cost more.
Their are instances when you don't need them. This is mainly in commercial buildings were the ceilings main structure is constructed from steel. If you have a false ceiling, your not necessariliy interfering with its fire integrity.
More information about fire rated downlights and Building Regulations can be found here.