Pinchas Gutter goes out of his way to find me biscuits. In a sun-baked living room in his north London home, he opens a packet of Rich Tea, sits down and tells me about the Holocaust. Gutter was seven years old when the second world war broke out. He lived in the Warsaw ghetto for three and a half years, took part in its uprising, survived six Nazi concentration camps – including the Majdanek extermination camp – and lived through a death march across Germany to Theresienstadt in occupied Czechoslovakia.