The mayor played in the film was in fact the son of the actual mayor when Crowhurst set sail. In fact the son has even been mayor of Teignmouth twice since his father. He is the 3rd generation of Bladons to serve as mayor to the town.
One of two biopics about Donald Crowhurst slated for release in the UK only a few weeks apart. The other, the independently produced Crowhurst (2017), starring Justin Salinger as Donald Crowhurst, was finished earlier, but the distributor of The Mercy bought it and delayed its release until a month after that of this film.