One of the richest and least known medieval libraries, the Parker collection at Corpus Christi College, Cambridge, will be rehoused and opened to the public for the first time in a £20m project announced yesterday.

There is room in the present library for just four scholars a day, and the public is never admitted.

For book enthusiasts the best chance of seeing one of the greatest treasures is when a new Archbishop of Canterbury is enthroned. The 6th century gospel given by Pope Gregory to Saint Augustine to take with him to convert the heathen English is then sent for a day to Canterbury Cathedral.

The library's extraordinary books include an 8th century Northumberland gospel, the two volume 13th century history of the world made by Matthew Paris at St Albans, which includes his drawing of the first elephant in England at the Tower of London, and the oldest known manuscript of the Anglo-Saxon chronicles, including an eyewitness account of the Battle of Hastings in 1066.

The collection of 600 manuscripts and 20,000 printed books was made in the 1560s by Matthew Parker, co-founder of the Church of England, archbishop of Canterbury and former master of the college. He was shocked by the carelessness of college libraries, and left his books to Corpus Christi with strings: if it ever lost 16 little books, 12 big books or six very big books, it would lose the bequest.

Parker collected his books in the wake of the destruction of libraries during Henry VIII's dissolution of the monasteries. Parker entered folklore as Nosey Parker, when, with a warrant from Queen Elizabeth, he sent his agents scouring the country to collect books.

The £20m will pay for a three-storey library with exhibition space, a conservation centre, and for digitisation - the entire collection is to be put on the internet.