What part does Mr. Shillitoe play in Miss Prior's decision to make regular visits to the prison in the novel, Affinity?

Mr. Shillitoe had been an acquaintance of Mr. Prior and had often come to dinner in their home. Based on a conversation with Mr. Shillitoe during one of these meals, Miss Prior decides to begin visiting Millbank Prison. Both Miss Prior and Mr. Shillitoe believe that visits from Lady Visitors to the prisoners can help the prisoners aspire to a life without crime.