This story is entirely untrue. Orson Welles had already completed "F For Fake" before starting work on the "Great Mysteries" television series. Far from being made cheaply, the "Great Mysteries" show was the most expensive British television series of 1973, utilizing the talents of many other American stars besides Welles, as well as top British talent. The idea that a drama series featuring top talent would be directed by a weather forecaster is, of course, preposterous. Burt Reynolds is described as being a "huge star" in 1971, when his major breakthrough as a leading man came the following year in "Deliverance". Also, Orson Welles had no agent; his contracts were arranged by his lawyer Arnold Weissberger (an elderly man in the early 1970s, who had represented Welles for over 35 years at that point).
Both Sean Biggerstaff and Robbie Coltrane are veterans of the Harry Potter film franchise.
This is the Final role of Robbie Coltrane before his Death.