The best suggestion. Fit a warm roof and eliminate loft ventilation.

Technically, it isn't a warm roof solution unless the Kingspan goes on top
of the rafters (perhaps with some between). 50mm on top and 50mm between
should be enough for a loft conversion, although I haven't got the tables in
front of me. This is only possible if you have a detached house and planning
permission, as it affects the roof line. The problem is that you can't fully
fill the rafters unless you have an equal thickness above them. You can't
have 75mm between and 25mm above, for example.

I suppose you would call my original suggested solution a warm loft, cold
roof.

Christian.