Rosen was born into a Jewish family in Harrow, Middlesex,[3] with roots in what are now Poland, Russia, and Romania[3] and connections to the Arbeter Ring and the Bund.[4] His father Harold (1919–2008) was born in Brockton, Massachusetts but grew up in the East End of London from the age of two, when his mother left his father and returned to the country of her birth.[5] He attended Davenant Foundation School and then Regent Street Polytechnic.[6] Harold was a secondary school teacher before becoming a professor of English at the Institute of Education in London,.[7]