Understanding British Library shelfmarks
The following explanation will help you understand how you can tell which books are available in the British Library reading rooms, which ones you need to order up, and which ones you can get on inter-library loan:
If the shelfmark of the item in the bibliography says:
London Reference Collection - the book can only be used in the reading rooms in London or Yorkshire, and you must request it using the British Library catalogue at http://catalogue.bl.uk When you request the item, it will say how long it takes to be delivered to the reading room (70 minutes or 48 hours, depending whether the item is stored in London or Yorkshire and whether you are using a reading room in London, or Boston Spa in Yorkshire).
London Reference Collection OPL - the book is on the shelves in the Social Sciences Reading Room at St Pancras, in the Reference Books OPL sequence. You must come to London to use it.
London Reference Collection SPIS - the book is on the shelves in the Social Sciences Reading Room at St Pancras, in the SPIS sequence. You must come to London to use it.
DS shelfmark - the book is a Document Supply item. You can either order it for delivery to the reading rooms in London, which takes up to 48 hours, or you can order it to be sent to you on inter-library loan through your university or public librarian or corporate account. See Document Supply for more details.