Icing!! Again!!!!!
Assuming Royal Flight was their 76...
All present S76's are NOT certified for icing. Therefore, there is no preferred temperature for icing.
As for the London weather at the time...........was precip present at the given OAT????
"ICE IS NOT NICE"!!!!
Freakin cold temperatures are a different story. The 76 is certified to -34 celsius as per the flight manual. Nick correct me if I'm off on that number.
DK