I have plenty of air flow below the tiles on the roof, which is important to prevent condensation. If you have a draft blowing through your spotlights then I guess you don’t have any insulation around them. I think you are supposed to create a box or hood for the lights and insulate around that if you can. If it’s not insulated properly then you’ll get a lot of cold air coming through the lights. This will also suck some warm air out of your room. As for the draft through the skirting. Any idea if it’s coming from above or below? If above then you could drill holes and squirt in some expanding foam near the top of the walls. That can really work. If it’s coming from the floor then foam around where the floor meets the wall would help (behind the skirting).