Something like this happened to me at an ATM in Stratford a couple of weeks ago. I was busy getting some cash out, when I heard a voice behind me say 'Excuse me, sorry to bother you...'. This immediately made me suspicious, I just covered the keypad & screen, held my hand up and said 'Bear with me'. Whoever it was just walked off.
http://stratfordobserver.co.uk/news/spate-distraction-thefts-prompts-police-warning/