A PRICELESS collection of rare books and ancient manuscripts, which were under threat due to a leaky roof, have been saved.

Horrified library staff had discovered mould growing on some of the precious books in the unique collection of 20,000 volumes housed in the library of Durham Cathedral.

Now, English Heritage has stepped in with a £65,000 grant to repair the roofs and guttering above the library - which was once the monks' refectory - and save the medieval manuscripts from further damage.

The Very Reverend Michael Sadgrove, Dean of Durham Cathedral, said: "The library, with its magnificent collection of medieval manuscripts and early printed books, is one of the cathedral's most precious assets, as are the buildings around the library.

"This grant is extremely good news both for the cathedral and for scholars who use the library."

The leak in the 19th Century lead sheeting that covers the roof was discovered during an inspection in 2004 by cathedral architect Christopher Downs.

Repairs done during the 1970s had split, rainwater was seeping into the library causing damp stains and peeling paintwork, and holes had appeared in the lead guttering.

The damp had already led to mould growing on several of the books, although the library's most precious pieces remained safely under lock and key - including the world's only copies of some 17th Century music manuscripts, irreplaceable antiquarian collections of the region's history and some of the country's oldest surviving printed books, dating to 1500.

Assistant librarian Joan Williams said: "Ancient books and manuscripts can deteriorate very rapidly in damp atmospheric conditions, so it was vital that the roof repairs were carried out as quickly as possible.

"We have already had to cover two of the bookcases with polythene sheets where water comes through the roof after very heavy rain."

Urgent repair work to make the buildings water-tight will now get under way.

Carol Pyrah, regional director of English Heritage, said: "Durham Cathedral is one of the most important and best-loved buildings in the region and forms a major part of the World Heritage Site.

"We are delighted to be supporting the cathedral with this grant."

The award to Durham was part of a £1m package of grants announced by English Heritage yesterday to support 25 cathedrals around the country.