The film's two writers and producers were both called Ronald - Ronald Wolfe and Ronald Chesney. As there was a TV series at the time starring Ronnie Corbett and Ronnie Barker called The Two Ronnies (1971) - the pair were nick-named both this and "The Two Ronalds".
Again there is much product placement on display: Jack places his bets with Ladbroke's (as seen on the side of both his bus and the Safari Park Special), whilst Mrs Butler is partial to a Guinness, as advertised on the No 12's side.