The collection began between 1836 and 1870 and grew from the receipt of books from legal deposit, from the acquisition of bequests and, in some cases, from requests made to the police following their seizures of obscene material.

From the nineteenth century, the subversive and libellous material was separated into the Suppressed Safe collection while the erotica and pornography were placed in a locked cupboard known as the Private Case.

Some of these were large: the book collector Henry Spencer Ashbee's 1900 bequest contained 1,379 volumes of erotica; the anthropologist Eric Dingwall—an honorary assistant keeper to the department of printed books—donated several works during his lifetime and at his death; and in 1964 the bibliophile Charles Reginald Dawes bequeathed 246 works of erotic literature.

[13] The process was continued by Panizzi's successor John Winter Jones, who did not inform the library's trustees or officials of the practice of withholding books from circulation.

[19] These included works such as The Crafty Whore (1658) by the Italian author Pietro Aretino (translated by Richard Head from the original Italian[20]); The Whore's Rhetorick (1683) by Philp-Puttanus (a pseudonym of the Italian writer Ferrante Pallavicino); A New Description of Merryland (1741) by Roger Pheuquewell (a pseudonym of Thomas Stretzer); The Natural History of the Frutex Vulvaria (1741) by Philogynes Clitorides; Teague-root Display'd (1746) by Paddy Strong-Cock; Matrimonial Ceremonies Display'd (1748); Harris's List of Covent Garden Ladies (1788–1790); The Cuckold's Chronicle (1793); and Paradise Lost; or The Great Dragon Cast Out (1838) by Lucian Redivivus.

[39][40][f] On his death, Rose bequeathed seven works of erotica to the library, including The Bride's Confession (1917); The Festival of the Passions (1863); and The Dialogues of Luisa Sigea (1890) by Nicolas Chorier.

[42][43] In 1950 the Private Case was expanded by the receipt of the Eliot–Phelips collection, formed by Edward Phelips, which had been held by the Guildhall Library, London.

Among the 33 works they received were Sodome (1888) and Gomorrhe (1889) by Henri d'Argis; Odor di Femina (1919) by Edmond Dumoulin; and Ma Vie secrète (1923).

[38][43] The last of these was a French translation of the English novel My Secret Life, possibly written by Ashbee or William Haywood.

[38][44] In 1946 the anthropologist Eric Dingwall was appointed honorary assistant keeper to the department of printed books of the British Museum, where he curated the Private Case.

Between 1951 and 1955 he acquired and donated 38 works, including Frank and Ich by Georges Grassal, Nini à Lesbos by Jacques des Linettes and 3 books pederastic in nature.

[47][43] One of the works Dingwall acquired for the museum was a first edition (1749) of Fanny Hill; Cross describes the book as "of exceptional rarity and historical importance".

[49] In 1964 the British Museum Library received a bequest of 246 works of erotic literature from Charles Reginald Dawes;[g] according to Cross, writing in 1991, "many scholars now consider to be of more importance than the Ashbee erotica collection".

[57] Until the 1960s the procedure to obtain access to Private Case material was exacting; the historian Alison Moore described it as "particularly labyrinthine".

[58] The reader would then be invited for interview to ascertain if they were a serious scholar with a legitimate and reasonable rationale to access the material and not—as one principal librarian described it—involved in "indiscriminate browsing in the field of erotica".

[34] In 2019 the contents of the Private Case were digitised and made available through the Gale subscription database Archives of Sexuality & Gender.

[64][65] Gale describes the Private Case material as "an interesting study in social ethics as the definition of obscenity evolved since the mid-19th century";[65] the British Library, while noting that nearly all the contents were "produced by heterosexual men for heterosexual men",[34] describes the works as a "unique insight into historic attitudes towards gender, sexuality and obscenity".

The move induced the lawyer and writer E. S. P. Haynes to produce "The Taboos of the British Museum Library", an essay in the literary magazine The English Review.

[66][67] Describing the existence of the Private Case as "unsatisfactory", he criticised the museum for censorship and wrote that "the reputation of our National Library is suffering in consequence" of the segregation of books.

[68] The library practice of keeping the names of Private Case books off the general catalogue he thought "a ruinous policy, and one which in the long run may prove suicidal.

[68] Despite Haynes's essay the wider public continued to be unaware of the existence of the Private Case until the 1960s and it was only in 1962 that the library acknowledged that it held a collection of books not included in the main general catalogue.

[69] The situation of the segregated books was not discussed more widely until 1963 when there was a debate in the correspondence pages of The Times Literary Supplement about the library's policy.

[74][75] The Bodleian Library at the University of Oxford classifies their collection as Φ (Phi)—a joke that a reader viewing the material may exclaim "Fie!

[83] The segregation of works has now been mostly lifted, although it continues only for explicitly illegal material, such as child pornography, Holocaust denial or serious copyright infringement.

[85] Although the figures of 25,000 volumes and 100,000 prints and drawings have been put forward,[86][87][88] Legman describes this as a "legend"[89] and the historian H. Paul Jeffers calls it "a persistent and false belief".