After his retirement, he returned to radio to produce John Arden and Margaretta D'Arcy's Whose is the Kingdom?,Whose is the Kingdom?, John Arden and Margeretta D'Arcy, Episode 1, 19 February 1988, BBC Genome a nine-play sequence of dramas about Christianity. Arden and D’Arcy wrote to The Irish Times after Mason's death, reporting that his funeral had needed to be postponed by a week to accommodate the people who wished to attend, and, in their tribute, gave an insight into his working practices: ‘As a drama director, he was a natural radio genius and an educator both to playwrights and actors. He never seemed to forget that he had begun his adult life as a teacher: he would inspire his casts by getting up from the directorial chair, moving all over the studio, telling stories, and more or less improvising the whole play from start to finish, with a running fire, of folklorish anecdotes from his childhood in County Antrim.’ Letters, Irish Times, 17 February 1997
