I can't find much record of him, but it would appear his name was Harman Hapgood:
http://genome.ch.bbc.co.uk/schedules/radio4/fm/1970-09-09
Contributors
Written By: Bruno Milna
Daniel Archer: Edgar Harrison
Doris Archer: Gwen Berryman
Jack Archer: Denis Folwell
Peggy Archer: June Spencer
Lilian: Elizabeth Marlowe
Tony Archer: Colin Skipp
Philip Archer: Norman Painting
Jill Archer: Patricia Greene
Christine: Lesley Saweard
Tom Forrest: Bob Arnold
Carol Tregorran: Anne Cullen
John Tregorran: Phillp Morant
Jack Woolley: Philip Garston-Jones
Walter Gabriel: Chris Gittins
Mrs Perkins: Paullne Seville
Gregory Salt: Gerald Turner
Nora Salt: Julia Mark
Lady Isabel Lander: Mary Wimbush
Brigadier Winstanley: Anthony Godfrey
Hugo Barnaby: Michael McClain
[i]Harman Hapgood: Geoffrey Lewis[i]
Zebedee Tring: Graham Rigby