Well here it is, this 1 video promises to be the 1 that gives me the most grief from both electricians and warm roof supporters.
we have used 1mm twin and earth for the lighting circuit and 2.5 twin and earth for the socket radial and heating circuit.
100mm insulation is fitted tight to the underside of the ceiling and this then eliminates any trapped air that may condensate, as is sometimes an issue in a cold roof.