Aged 20, Hazeldine made his London debut at the Royal Court Theatre in Sloane Square. Initially hired to understudy as Cliff in "Look Back In Anger", Hazeldine soon started taking on small roles in Edward Bond's "Narrow Road to the Deep North" and "Early Morning". He worked constantly at the Royal Court during the 1969–1970 season. Spotting Hazeldine's potential, Peter Gill then cast him in his play "Over Gardens Out" and went on to direct him in "Crete and Sergeant Pepper" by John Antrobus.