 The mother and son characters of Ursula and Alistair Gooding are  related (as sister and cousin respectively) to Iris and Dennis  Rainbird (again mother and son), characters in the very first  episode,  _"Midsomer Murders" (1997) {The Killings at Badgers Drift (#1.1)}_ (qv).  Both sets of characters were played by Elizabeth Spriggs (qv) and  Richard Cant (qv).