50 Berkeley Square — the room in Mayfair that supposedly frightens people to death

Posh as it gets, Berkeley Square, Mayfair, central London. Number 50. Grade II listed, used to be PM George Canning's gaff. And for a stretch in the late 1800s it had the reputation as THE most haunted house in London. It's the attic room. The stories don't even agree which is half the fun — most s……