Alan's mother4 was also the product of generations of empire-builders, being descended from a Yorkshireman, Thomas Stoney (1675-1726) who as a young man acquired lands in England's oldest colony after the 1688 revolution, and who became one of the Protestant landowners of Catholic Ireland. His estates in Tipperary passed down to his great-great-grandson Thomas George Stoney (1808–1886), who had five sons, the eldest inheriting the lands and the rest dispersing to various parts of the expanding empire. The third son was a hydraulic engineer, who designed sluices for the Thames, the Manchester Ship Canal and the Nile; the fifth emigrated to New Zealand, and the fourth, Edward Waller Stoney (1844-1931), Alan's maternal grandfather, went to India as an engineer. There he amassed a considerable fortune, becoming chief engineer of the Madras and Southern Mahratta Railway, responsible for the construction of the Tangabudra bridge, and the invention of Stoney's Patent Silent Punkah-Wheel.

A hard-headed, grumpy man, Edward Stoney married Sarah Crawford from another Anglo-Irish family, and they had two sons and two daughters. Of these, Richard followed his father as an engineer in India, Edward Crawford was a Major in the Royal Army Medical Corps, and Evelyn married an Anglo-Irish Major Kirwan of the Indian Army. Alan's mother, Ethel Sara Stoney, was born at Podanur, Madras, on 18 November 1881.

Although the Stoney family did not lack for funds, her early life was as grim as that of Julius Turing. All four Stoney children were sent back to Ireland to be educated. It was a pattern familiar to British India, whose children's loveless lives were part of the price of the Empire. They were landed upon their uncle William Crawford, a bank manager of County Clare, with two children of his own by a first marriage and four by a second. It was not a place for affection or attention. The Crawfords moved to Dublin in 1891, where Ethel dutifully went to school each day on the horse-bus, crushed by a regimen that permitted her a mean threepence for lunch. At seventeen, she was transferred to Cheltenham Ladies College, 'to get rid of her brogue,' and there she endured the legendary Miss Beale and Miss Buss, and the indignity of being the Irish product of the railway and the bank among the offspring of the English gentry. There remained a flickering dream of culture and freedom in Ethel Stoney's heart and for six months she was sent, at her own request, to study music and art at the Sorbonne. The brief experiment was vitiated by the discovery that French snobbery and Grundyism could equal that of the British Isles. So when in 1900 she returned with her elder sister Evie to her parents' grand bungalow in Coonoor, it was to an India which represented an end to petty privation, but left her knowing that there was a world of knowledge from which she had been forever excluded.