Complex sentence: He held membership in many London clubs and founded his own club in Edinburgh, called Puffin's, after his first wife, Diana Hay, 23rd Countess of Erroll, whom he married on 19 December 1946 at St Margaret's, Westminster.
Split into simpler sentences: He held membership in many London clubs and founded his own club in Edinburgh, called Puffin's. Firstly Diana Hay, 23rd Countess of Erroll, whom he married on 19 December 1946 at St Margaret's, Westminster.