In all the years I worked at Heathrow I only experienced snow on a handful of occasions but, of course, plenty of occasions when there was ice. I don't know the technical details but following one forecast of freezing conditions they sprayed a runway.... with the wrong mixture and 27L immediately changed into a skating rink!!
The place simply couldn't cope with snow (hopefully it's changed now). We used to sit back watching the Fred Karno goings on and wonder what the Canadian and Scandinavian crews thought of the place.