He was born in Bloomsbury. His mother was Anna Wickham the poet, a fiercely unconventional woman who appears to have despised her husband's suffocating conventionality. Jim's father, Patrick, was a lawyer, and, as President of the British Astronomical Association, a world authority on the planet Saturn. He learnt Hebrew in order to translate the Psalms and was a reckless fell-walker who died trying to get to Borrowdale from Grasmere on Christmas Day. He was, perhaps, unconventional in everything but in his insistence that Anna play the role of model housewife.
From 1909 the family lived in a house in Downshire Hill, Hampstead, where D.H. Lawrence and Edith Sitwell were regular visitors. One of Jim's earliest memories was of himself and two other small boys parading round one of Anna's garden parties in the summer of 1914, each holding up a placard: one read "VOTES", the next read "FOR", and the third "WOMEN".
In 1919 they moved to Parliament Hill, where Hepburn was to live for the rest of his life. House guests were numerous and included Malcolm Lowry, Lawrence Durrell and Dylan Thomas. The bathroom (which doubled as an aviary) inspired the opening of Dylan Thomas's 1955 story Adventures in the Skin Trade.
When her youngest son died from scarlet fever, Anna whisked her eldest off to Paris for six months, to rub shoulders with Ezra Pound, Sylvia Beach, Djuna Barnes and Nina Hamnett, who painted a portrait of him. One evening at the Dome, he beat Aleister Crowley at chess - thus incurring the fury of the Beast.
In 1927, Jim Hepburn appeared at the Hippodrome in Hit the Deck, starring Stanley Holloway and Jesse Matthews. Through his mother's friend Augustus John, he met C.B. Cochran and the following year became Noel Coward's understudy in This Year of Grace, which also starred Beatrice Lillie. During the run in New York, Jim took lessons in the latest tap-dancing techniques and on his return to England taught them to his brother John. The two tap-danced their way through the music-halls of the Thirties as "The Two Madisons" (billed as "Red Hot Terpsichore"). In 1935 Matthew Norgate wrote in the London Evening Standard that the "Two Madisons and Sonia" were remarkable for the fact that they actually managed to make tap-dancing interesting.
When war broke out, "The Hepburn Brothers" (as they were now called) signed up immediately. Jim joined the RAF and found himself acting as navigator owing to a knowlege of astronomy picked up from his father. He flew with 216 bomber squadron in North Africa, once making a forced landing in the desert during a sandstorm. In 1943 he was awarded the DFC.
After the war, Hepburn helped pioneer the idea of freight aviation by flying round the world. In 1948 he started Eagle Aviation with Harold Bamberg and joined in the Berlin airlift, flying 28 round trips in 10 days.
In 1950 he married Margaret Telfer, a woman with something of his mother's strength of character, and decided that family life was incompatible with operations flying. He joined the Ministry of Defence, where he worked until 1977 without ever saying exactly what he did - although local rumour had it that his was the finger poised over the nuclear button. This was almost certainly not true, but one could imagine if someone were to have that job it might well be a man as steady, trustworthy and true as Jim Hepburn.
In later life he instigated the literary revival of his mother's poetry and became a home brewer of beer par excellence. He was a cornerstone of the Hampstead Labour Party, and claimed that his remaining ambition was not to die under a Tory government.
James Geoffrey Cutcliffe Hepburn, tap-dancer, air force officer and civil servant: born London 3 November 1907; DFC 1943; married 1950 Margaret Telfer (nee Hope; one daughter, two stepdaughters); died London 15 December 1995.