Evelyn Waugh's Edmund Campion and "Lady Southwell's Letter"

[Extract]In the "Author's Note" to the first edition of Edmund Campion: A Biography, Evelyn Waugh wrote: "Father Watts of Stonyhurst lent me a copy of Lady Southwell's letter, preserved in the library there, describing the death of Queen Elizabeth" (1st ed. ix). And the biography opens with four vivid pages portraying the Queen as "an old perjured woman, dying without comfort". Intriguingly, the reference to "Lady Southwell's letter" is omitted from all later editions. Nor do the "Notes" or the "List of Books Consulted" (which appear in the First and Second editions) mention Southwell. Nor did Waugh alter the first four pages after he dropped the reference