The letter from Lady Gwendoline Bertie, written in August 1907, was found by Cambridge academic Dr Warren Dockter, the Telegraph reports.
Lady Gwendoline, who married Churchill's brother Jack in 1908, writes: "Please don't become converted to Islam; I have noticed in your disposition a tendency to orientalise, Pasha-like tendencies, I really have. If you come into contact with Islam your conversion might be effected with greater ease than you might have supposed, call of the blood, don't you know what I mean, do fight against it."
