A 12th century manuscript, which will be displayed in Rochester Cathedral, is to be included in the 800th anniversary commemorations of the Magna Carta.

The Magna Carta was agreed between King John and his barons in 1215, starting the process which brought constitutional law and freedoms to England.

However, almost 100 years earlier, a single scribe had written The Textus de Ecclesia Roffensi per Ernulphum episcopum (The Book of the Church of Rochester through Bishop Ernulf), usually referred to as the Textus Roffensis.

The medieval book contains two manuscripts: a collection of documents including the Law of Ethelberht who was the King of Kent from 560 to 616AD, and the oldest of the Rochester Cathedral registers.

The Law of Ethelberht is the oldest surviving English law code and the oldest Anglo-Saxon text in existence.

The Textus Roffensis is set to be displayed in the crypt of Rochester Cathedral as part of the £5.7m Hidden Treasures, Fresh Expressions project which is expected to open in July 2015.

The exhibition will include glass viewing panels in the floor, touch-screen displays and room for the Cathedral’s collection of old photographs and slides, previously hidden from the public.

The project will form part of the Magna Carta Trails, five trails across the country which allow people to explore locations that are connected with the famous charter.

The Kent Trail includes Rochester, Faversham, Canterbury and Dover.

Over the centuries, the Textus Roffensis has been lent, lost and then found and has been in the custody of a variety of different people and places.

It is now held at the Medway Archives Office in Strood.

Sometime between 1708 and 1718 the book was immersed for several hours in either the River Medway or the River Thames when the ship transporting it overturned and water damage is apparent on a number of pages.

The book has been named as Britain’s Hidden Treasure by the British Library.