Shyte, concur
And for all, the icing 'clearance!' of the Mk2 was +4 deg C. The surface temp was +9 giving a ceiling to the flight (by rule of thumb) 2500'. SALT was 2800'. Next leg SALT 5900' (Ben Nevis)
Interesting that Day in the HoL presentation tried to imply a surface temp of +11 (which it was at Machrihanish)
I would point questioners to the Mil Archives for the past arguments.