A £9m appeal has been launched by the British Library to buy the oldest intact book in Europe, a palm-sized leather-bound copy of the gospels buried 1,300 years ago in the coffin of Saint Cuthbert.

The Cuthbert Gospel, on loan to the library since 1979, is regarded as of such importance that the National Heritage Memorial Fund has raided its reserves to offer a £4.5m grant, half the purchase price and the largest single acquisition grant in the library's history. The Art Fund and the Garfield Weston foundation have each promised £250,000.

If the appeal succeeds, the library has agreed the gospel will be displayed half the time at Durham cathedral, where it was found with the body of the saint when his coffin was reopened in 1104.

The gospel is still in its original 7th century leather cover, which has survived in perfect condition.