Down lights can be anything from 2 inches to 2 foot, and 12 volt (extra low voltage) to 230 volt (low voltage) as to what is normal, I don't know.
With extra low voltage some where you need to reduce the voltage from low voltage, toroidal or electronic transformers, or drivers, with low voltage it needs RCD protection and earth bonding of some sort.
Rules change country to country, Wales and England are not the same, there does not seem to be anything wrong with what you propose, but since you don't really say what you intend to do, can't really give an answer.
Also the word "I" tells us nothing, and because I can do some thing it does not mean you can.