Electrical wiring under boards on top of loft insulation

If your changing the use of the room then the wiring within it would need to meet the regulations expected of that room. Current carrying capacity of electric carrying cables is one factor that electricians need to account for when calculating circuits and this changes depending on what material they are in contact with. As current travels through a wire it begins to heat up relative to the resistance and current in the cable. If the heat cannot escape then there is the potential for the insulation to melt. For example the safe carrying capacity drops for a cable when it is surrounded by insulation as opposed to when it is in free air, and also in your case when it is pressed up against another surface. I would say the current carrying capacity of the cables will have dropped if they are now in a more enclosed environment. If you are very concerned about it then you should have an electrician visit on site to give you their opinion and perhaps issue a certificate for the work even though the changes are rather superficial.