The article explains that Robert Gottlieb, the book’s editor at Simon & Schuster, tried to obtain blurbs from established authors. Waugh was among those solicited, with somewhat disappointing results – but not quite as disappointing as you would conclude from the Guardian article. Here’s what the article says:
Gottlieb’s enthusiasm inspired him to send out advance copies, a strategy that (as so often) did not always work. Evelyn Waugh wrote back: “You are mistaken in calling it a novel. It is a collection of sketches – often repetitious – totally without structure.”
In fact, Waugh’s response, reproduced in Letters, pp. 571-71, starts by expressing his thanks for the book and his sorrow that Simon & Schuster found it so fascinating. He notes his belief that the book was both indelicate and prolix and concludes his objections to the novel with the passage quoted above, but he then continues:
Much of the dialogue is funny.
You may quote me as saying; ‘This exposure of corruption, cowardice and incivility of American officers will outrage all friends of your country (such as myself) and greatly comfort your enemies.’
A backhanded assessment which I doubt appeared on the book’s cover, but at least Waugh recognized its humor. Waugh must have gone to the trouble of reading it through because he recommended that it be reduced by half and urged that “the activities of ‘Milo [Minderbinder]’ should be eliminated or greatly reduced.” Notwithstanding Waugh’s reservations, the book has remained in print and sold over 10 million copies.