I flew daytime HKG to LHR in business class before and the F/As did not force any passenger to close any windows.

Not many passengers are sleeping through the flight. In general they only sort of close windows on overnight flights especially on summer time, when sun rises early over Europe. Also on midnight flights from HKG to West Coast of North America/Australia/NZ! Basically on those flights that passengers will sleep through the flight. On flights that are mostly daylight, like Australia/NZ to HKG daytime, they really don't force you to close the windows.

Carfield