<<You are in ATC, I presume?
Low vis procedures require greater inbound spacing, and thus slow down arrivals - they very thing that LHR cannot afford to do. Less arrivals = more cancellations.>>
Retired after 31 years dealing with Heathrow traffic. LVPs slow down traffic anywhere, not just Heathrow. There's nothing much one can do about fog, but it doesn't happen every day.