An account of his years in California was written up in his first book, Educating William; Memoirs of a Hollywood Correspondent, in which Cash chronicled his adventures as a British journalist in America and his encounters with such figures as David Hockney, Elizabeth Taylor, Hunter Thompson, Tom Wolfe, Jay McInerney, and Antony Haden-Guest.
In 2000, Cash wrote a play, The Green Room, about the life and hospital death of the English linguistic philosopher A. J. Ayer, which opened at the Cockpit Theatre in London and was selected as a Critics' Choice of the Edinburgh Festival by The Observer.
In 2014, Cash made a submission to the planning minister Greg Clark, arguing for stronger safeguards to protect heritage in the NPPF.
It was described by Tatler as "Immensely readable... Laugh-out-loud funny…a delightful true story of love, hope and redemption by one of the foremost society writers of our day".
He is the founder of Spear's business and culture magazine whose majority stake was sold to Mike Danson of Progressive Digital Media in 2010.
Cash resigned as a director to focus on being editor-in-chief of The Mace, a new cross-party politico and public affairs magazine covering Westminster and Brussels.
These include leading a Catholic Herald pilgrimage along the Via Francigena to Rome to commemorate the canonisation in Rome of Saint John Henry Newman in October 2019; walking the St Cuthbert's Way from Melrose Abbey to Lindisfarne and walking 140 miles along the Pilgrims' Way, from Winchester to Canterbury in the footsteps of Hilaire Belloc in July 2020.
[21] Cash lives at Upton Cressett Hall, Bridgnorth, Shropshire, which he renovated in 2008–2010, hiring the artist Adam Dant to paint a series of six neo-Elizabethan murals which were described as 'daring and original' by John Goodall, architectural editor of Country Life.
[22] His family members include the Second World War hero Captain Paul Cash MC and the 19th-century Liberal politician John Bright.
He is a distant cousin of the American country singer Johnny Cash, whose family sailed from England and settled in Salem, Massachusetts, in 1667.