"One day we were in the make-up trailer and someone was brushing out Benedict’s stunt double’s wig - and we decided to put Martin in it. We put Sherlock’s coat on him and stood him on top of one of the make-up chairs so he looked tall and took the photo from low down. And when Benedict came in we got the make-up assistant to ask him to autograph the photograph. She handed it over - and this is how Benedict’s mind works - and he went “I don’t remember wearing my coat with that colour scarf"