Heathrow’s Rail stations have the normal yellow line but they have a blue line further in to advise people to stand behind and people mostly follow it.
Originally it was for social distancing but now it’s to allow a corridor for people to move down the platform in, not putting themselves or their luggage close to the platform edge. It does seem to work quite well.
I suppose somewhere like Heathrow where a considerable number of people are travelling with large suitcases, might be an exception to the overall plan.