This column has often remarked that one of the best ways of making an A-grade radio feature is to assemble several elderly upper-class ladies in a BBC studio and encourage them to reminisce. If, as was the case in Tessa Dunlop’s illuminating documentary about Bletchley Park (22 July), they happen to have been engaged in wartime code breaking, then so much the better, for that characteristic note of self-deprecation strikes so much the louder when the person involved has just got wind of, as it may be, the Italian retreat from North Africa.My second favourite among the five survivors (ages varied from 89 to 97) of the world of Turing, Enigma and the “Colossus” computer was Rozanne Colchester, recruited on the strength of her facility with the Italian language. The daughte