A first edition of Charles Darwin's groundbreaking 'Origin Of Species', which languished for years in a toilet in Britain, will go under the hammer this week, on the 150th anniversary of the book's publication.

Christie's auction house said the book, estimated to reach £60,000 (NZ$136,000), was bought by a family for just a few shillings in a shop in the West Country about 40 years ago.

It has since been kept on a bookcase in the guest lavatory at their home in the Oxford area.

Christie's said the son-in-law of the current owners was at an exhibition on Darwin and spotted a picture of the spine of the work.

He realised his in-laws' book was something special, matching the binding in the picture.

"The book is incredibly important," said, Margaret Ford, head of books and manuscripts at Christie's.

"He knew it (the book) was textually important. (But) he maybe did not know how much of a bargain he was getting."