By law, a copy of every UK print publication must be given to the British Library by its publishers, and to five other major libraries that request it. This system is called legal deposit and has been a part of English law since 1662. From 6 April 2013, legal deposit also covers material published digitally and online.

The Legal Deposit Libraries include:

• the British Library
• the National Library of Scotland
• the National Library of Wales
• the Bodleian Libraries, Oxford
• the University Library, Cambridge
• the Library of Trinity College, Dublin

The benefits of Legal Deposit to you as an author are numerous. Deposited publications are made available to users of the deposit libraries on their premises, are preserved for the benefit of future generations, and become part of the nation’s heritage. Publications are recorded in the online catalogues, and become an essential research resource for generations to come. Most of the books and new serial titles are listed in the British National Bibliography (BNB), which is used by librarians and the book trade for stock selection.
The British Library is entitled to delivery, free of charge, of one copy of every publication within one month beginning with the day of its publication. The British Library will issue a receipt when your book is deposited.

Source: The British Library, 2018.