As we chat casually between shots, she tells me about the odd times, usually in Europe, when she's feared for his safety after being surrounded by mobs of Potter-mad teens, and it's only then that you realise just how … (In fact it's rammed home throughout the day as we shoot in the street outside the East London studio we're in, when a group of builders and then two police cars full of policemen turn up to pretend not to watch).