Season 1 BBC One , 1968 Watch now Season 2 BBC One , 1968 - 1969 Season 3 BBC One , 1969 Season 4 BBC One , 1971 Season 5 BBC One , 1971 Season 6 BBC One , 1972 - 1973 Season 7 BBC One , 1974 Season 8 BBC One , 1976