My Mum and Dad came to London to visit me from Scotland. It was Christmas time and their suitcases were heavy with presents. They are pensioners and my Mum struggled with her bag. As she dragged it up the stairs in the crowded underground, someone from behind lifted it, helping her to the top of the stairs. She said when this person lifted her case, it was such a relief, a little angel in the underground. At the top when she turned around to say thank you, the person had already disappeared.