In her essay ‘A House of One’s Own’, about Vanessa Bell, Janet Malcolm says memorably that Bloomsbury is a fiction, and that compared with letters and first-hand material, biography is like canned vegetables compared with fresh fruit.

We read the letters of writers because they are informal, unguarded, unbuttoned, intimate and candid, revealing not only the secrets of composition but, we hope, glimpses of the writer in the flesh, with his trousers down.