Coming to London in 1934, he rapidly made initial contacts in the literary world. A short study Middleton Murry: A Study in Excellent Normality (1934) brought him for a time into John Middleton Murry's Adelphi commune at "The Oaks", where in 1935 he worked as a cook. In 1935, also, he met Dylan Thomas, sent to meet him by Sir Richard Rees of the Adelphi magazine. In short order he became a Catholic convert, and married Margaret Edwards in 1937. In the mid-1930s he was influenced by Eric Gill.
He was a friend of George Orwell, encountered also in 1935 through Thomas and Rees, and later wrote about him in his memoir Four Absentees. Heppenstall, Orwell and the Irish poet Michael Sayers shared a flat, in Lawford Road, Camden. Heppenstall once came home drunk and noisy, and when Orwell emerged from his bedroom and asked him to pipe down, Heppenstall took a swing at him. Orwell then beat him up with a shooting-stick, and the following morning told him to move out. Friendship was restored, but after Orwell's death, Heppenstall wrote an account of the incident called The Shooting-Stick.
In an interview for the book World Authors, Heppenstall stated he had once been a left-winger, but since the 1960s had become more politically conservative. Heppenstall also said he was especially opposed to "Progressivism" and World Government. He listed Jorge Luis Borges, Samuel Beckett, and Vladimir Nabokov as the writers he most admired.
Heppenstall's first novel The Blaze of Noon (1939), was critically praised.  Much later, in 1967, it received an Arts Council award. He was Francophile in literary terms, and his non-fiction writing reflects his tastes.
Critical attention has linked him to the French nouveau roman, in fact as an anticipator, or as a writer of the "anti-novel". Several critics (including, according to his diaries, Hélène Cixous) have named Heppenstall in this connection. He is sometimes therefore grouped with Alain Robbe-Grillet, or associated with other British experimentalists: Anthony Burgess, Alan Burns, Angela Carter, B. S. Johnson, Ann Quin, Stefan Themerson and Eva Figes. The Connecting Door (1962) is singled out as influenced by the nouveau roman.
He was certainly influenced by Raymond Roussel, whose Impressions of Africa he translated. Later novels include The Shearers, Two Moons and The Pier. He also wrote a short study of the French Catholic writer Léon Bloy (Cambridge: Bowes & Bowes, 1953).
From 1945 to 1965, he worked for the British Broadcasting Corporation on radio as a feature writer and producer, and then for two further years as a drama producer. One of his early adaptations was of Orwell's Animal Farm in 1947.
In his journals, Heppenstall mentions problems he had with Evelyn Waugh regarding a radio broadcast in the 1940s. Waugh apparently felt that Heppenstall purposely insulted him when he was sent to take him to the broadcast.
Later in his life Heppenstall moved to the town of Deal. During this time he took a strong dislike to his working-class neighbours and began deliberately lighting bonfires in order to antagonise them. Heppenstall's final novel. The Pier, depicts a writer resembling himself murdering a similar family living next door to him.
After his death, Heppenstall's journals were published: they caused some controversy by revealing Heppenstall's hostility to fellow writers such as Alan Sillitoe and also expressing prejudices against blacks, Irish, Arabs and lesbians.
- Middleton Murry: A Study in Excellent Normality (1934)
- First Poems (1935)
- Apology for Dancing (1936) ballet
- Sebastian: New Poetry (1937)
- Poems (1938) with Lawrence Durrell, Ruthven Todd, Patrick Evans, Edgar Foxall, and Oswell Blakeston
- The Blaze of Noon (1939) novel
- Blind Men's Flowers Are Green (1940) poetry
- Saturnine (1943) novel, reissued as The Greater Infortune (1960)
- Poems, 1933–1945 (poems) (1946)
- The Double Image: Mutations of Christian Mythology in the Work of Four French Catholic Writers of To-Day and Yesterday (1947)
- Imaginary Conversations: Eight Radio Scripts (1948)
- Three Tales of Hamlet (1950) with Michael Innes
- The Lesser Infortune (1953) novel
- Léon Bloy (1953)
- My Bit of Dylan Thomas (1957)
- Architecture of Truth: The Cistercian Abbey of Le Thoronnet in Provence (1957)
- Four Absentees: Dylan Thomas, George Orwell, Eric Gill, J. Middleton Murry (1960)
- The Fourfold Tradition: Notes On the French and English Literatures, with Some Ethnological and Historical Asides (1961)
- The Woodshed (1962)
- The Connecting Door (1962)
- The Intellectual Part: An Autobiography (1963)
- Raymond Roussel: A Critical Study (1966)
- The Shearers (1969)
- A Little Pattern of French Crime (1969)
- Portrait of the Artist as a Professional Man (1969)
- French Crime in the Romantic Age (1970)
- Bluebeard and After: Three Decades of Murder in France (1972)
- London Consequences (1972) with Margaret Drabble, B. S. Johnson, Eva Figes, Gillian Freeman, Jane Gaskell, Wilson Harris, Olivia Manning, Adrian Mitchell, Paul Ableman, John Bowen, Melvyn Bragg, Vincent Brome, Peter Buckman, Alan Burns, Barry Cole, Julian Mitchell, Andrea Newman, Piers Paul Read and Stefan Themerson.
- The Sex War and Others: Survey of Recent Murder, Principally in France (1973)
- Reflections on the "Newgate Calendar" (1975)
- Two Moons (1977)
- Tales from the "Newgate Calendar" (1981)
- The Master Eccentric: The Journals of Rayner Heppenstall, 1969–1981, ed. Jonathan Goodman (London and New York, Allison & Busby, 1986), 278 pp. ISBN 0-85031-536-0
- The Pier (1986)
- Buckell, G. J. (2007). Heppenstall – A Critical Study (DAP). ISBN 1-56478-471-1 : ISBN 978-1-56478-471-1
- John Wakeman, World Authors 1950-1970 : a companion volume to Twentieth Century Authors. New York : H.W. Wilson Company, 1975. ISBN 0824204190. (pp. 632-34).
- Buckell, p. 15.
- J. P. Carswell (1978), Lives and Letters: A. R. Orage, Katherine Mansfield, Beatrice Hastings, John Middleton Murry, S. S. Koteliansky, 1906–1957, pp. 247–249.
- Andrew Lycett, Dylan Thomas: A New Life (2003), p. 130.
- Lycett, pp. 146, 175.
- Fiona MacCarthy, Eric Gill (1989), pp. 162, 269.
- Gordon Bowker, George Orwell (2003), p. 164.
- Bernard Crick: George Orwell: A Life, 1982
- Robert Hewison, Under Siege: Literary Life in London 1939–45 (1977), p. 62.
- Clair Wills, That Neutral Island (2007), pp. 158–9.
- Francis King, "The loneliness of a long- distance hater" (Reviews of The Master Eccentric and The Pier by Rayner Heppenstall). The Spectator, 6 December 1986, (p. 44-5).
- Buckell, p. 38.
- Randall Stevenson, The Last of England?, Oxford English Literary History, vol. 12, p. 408.
- George Orwell: A Kind of Compulsion 1903–1936 (1998), p. 378.
- "Having moved to Deal, Heppenstall was soon on equally dire terms with his neighbours there, deliberately lighting bonfires in order to annoy them." King 6 December 1986.
- John Carey, The intellectuals and the masses : pride and prejudice among the literary intelligentsia, 1880-1939. London : Faber and Faber, 1992. ISBN 0571162738 (p. 209-210)
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- Archival Material at Leeds University Library