Inferno
The vast majority of the studio sequences in Inferno were directed, uncredited, by producer Barry Letts as Camfield had been hospitalised by a heart complaint. Camfield was so upset by this and worried about his prospects of working again if it got out that he had a heart condition that Letts swore not to tell his BBC bosses and directed the remainder of the serial uncredited.
Camfield did return to Doctor Who to direct a Tom Baker story, but afterwards his wife made him swear on the alter of Ely Cathedral that he would never do another Doctor Who as she was scared it would kill him!.
Incidentally Graeme Harper could be said to be a progeny of Camfield and they certainly share same directorial flair and energy.