A rare book of Shakespeare's plays, considered to be one of the most important in British literature, is to be auctioned at Sotheby's in London. The complete first folio of the playwright's work had a print run of approximately 750 in 1623.

However, only a third of these survive and most of them are incomplete.

The book is being sold by Dr Williams's Theological Library in London, which hopes the proceeds - expected to be more than £3m - will secure its future.