HD,
I think you'll find that the definition of a WX Stby has not changed significantly for the past 25 years or more. If
Weather conditions make it difficult for ATC to
observe aircraft taking off or landing, MATS Part 1 requires them to initiate a Wx Stby. Therefore during LVPs, a Wx Stby is likely (though not always) to be required.
Perhaps Heathrow has its own procedures, that cover this requirement, without ATC initiation?
At ATC units where sight lines are obscured for other reasons, SRG will require appropriate procedures to be in place, and may even insist that the Airport Authority build a new Control Tower!
