Geoffrey Clifton is loosely based on the young, British baronet Robert Clayton-East-Clayton.
Clayton overheard of Almasy's search for Zerzurra at a dinner party, and was captivated by the idea. He made contact with Almasy, and joined the desert expedition of 1932, providing part funding and use of his Gypsy Moth plane. He brought his new wife (of two weeks) with him to the desert.
Like in the novel, Sir Robert did die young, at the age of 24. Only a few months after returning to England he died from an infectious disease contracted in the desert.
During the 1932 expedition Sir Robert wrote in his diary, and later reported to the Geographical Society. The expedition did not go according to plan, and this quote gives you an insight into his humour and goodnaturedness:
(1) Never trust an Arab guide; (2) always carry enough petrol to get back to your starting-place; (3) keep notes of every journey (it was Penderel's notes that gave us a clue to where we were); (4) take glasses; (5) never forget that the desert is always waiting to hit you below the belt, so don't give it the chance.
Robert Clayton-East-Clayton, Geographical Journal. Vol. LXXI, No. 3, p. 252.
For more information on the desert explorers and their expeditions, I would highly reccomend Fliegel Jezerniczky's wonderful website.
I would also highly reccomend the two authorative books on the period:
The Hunt For Zerzurra by Saul Kelly
The Secret Life of Laszlo Almasy by John Bierman