"They're changing Guard at Buckingham Palace…" begins the famous poem by AA Milne, creator of the much-loved children's character, Winnie the Pooh.   But it's not usually like this. The Grenadier Guards are now taking their posts at the Palace without the usual music and ceremony. It's what's known as "an administrative Guard mount"; used usually when there is heavy rain or a timing conflict with another important event. Now it's part of the government's social distancing policy -