An unexpected treasure has been discovered by two sharp-eyed charity bookshop volunteers.

Christine and Robert Williams were sorting through the latest delivery of donations to the National Trust’s second-hand bookshop at Mottisfont,when they came across a small, hardback book, complete with beautifully illustrated dust jacket.

It was a rare 1956 first edition of the children’s novel, The Last Battle, by C.S. Lewis, which could be worth £1,000.

The books is the last in the famous Chronicles of Narnia series and won the author the Carnegie Medal.

It is illustrated by Pauline Baynes, who was also J.R.R. Tolkien’s favourite illustrator.

“I think we knew we had something special as soon as we picked the book up,” says Christine.

“It was in excellent condition, though obviously quite old, with the most beautiful images on the jacket and inside. When we realised it was not a re-print, we were pretty excited!”

Christine and Robert are self-taught book valuers, but they sought professional verification of their find from an expert at their local auction house.

The book is now going to auction through Woolley & Wallis at Salisbury on June 17 (lot 33), with an estimate of £700 - £1,000.

The auction house is kindly waiving its usual fees, and the sale proceeds will go towards Mottisfont’s ongoing programme of conservation. For further details, contact Woolley & Wallis on 01722 424500 or visit www.woolleyandwallis.co.uk.