Warren started his photographic career at the age of 17 when he was acting in Alan Bennett's play Forty Years On with John Gielgud in the West End at the Apollo Theatre.
Warren začal svou fotografickou kariéru v 17. letech, když hrál ve hře Alana Bennetta Forty Years On s Johnem Gielgudem v londýnském West Endu v divadle Apollo.