This series was first shown in May/June 1976, about 18 months after John Gregson's death in January 1975 from a heart attack. Given that the series appears to have been filmed during a summer or autumn, it may have been filmed in 1974 and its release delayed for almost two years - perhaps as a mark of respect for Gregson's untimely death.
Bill Kirby's car was a 1957 Riley Pathfinder 2.5 litre, registration number 45 MMK.
The full names of the main characters were: Bill Kirby, Laura Marshall, Roger Fane, Claire Kirby and Robin Kirby. The credits only listed either first names or surnames for these characters.