The Earl of Macclesfield has welcomed a 6.4m deal to buy Britain's most important archive of papers relating to physicist Sir Isaac Newton, writes Andrew Ffrench.

The privately-owned collection includes documents, notebooks and letters on key scientific and mathematical matters such as gravitation, calculus and optics.

If Cambridge University fails to raise the money, the papers could be split up and dispersed throughout the world.

The Heritage Lottery Fund has promised 75 per cent of the 4.79m cost on the understanding that the University finds the rest. The archive was bequeathed to the first Earl of Macclesfield, Thomas Parker, by Welsh mathematician William Jones who died in 1749. Mr Jones taught Thomas and his son George.

Since then it has been kept in the library at the Macclesfield family seat, Shirburn Castle near Watlington, in south Oxfordshire. The earl, who admitted that 6m was a 'lot of money', said: "The papers are fading with age and preserving them requires modern conservation techniques. Newton is a national icon and this decision has been taken in the interests of national heritage." The Oxford graduate, who went to Worcester College, added: "There are already some Newton papers at Cambridge that is the best place for them."

The archive includes signed letters and working papers sent between Newton and his associates in discussion of various theories, many of which are written in Latin, as well as Newton's personal notebooks.

Peter Fox, university librarian at Cambridge, said: "If we can't raise the money, the collection could go abroad and be split among private collectors. That would be a tragedy for scholars and a great loss to the nation."