A historic diary written by a prominent Jacobite as he plotted the 1715 rebellion has been severely damaged while in the care of the British Library, The Times has learnt.

Its private owner, a descendant of Thomas Tyldesley, the diary’s author, has described how he “wanted to weep” when he collected the 96-page manuscript last week and discovered that someone had spilt oil across its pages –- staining them and making some of them completely illegible. Its original leather front cover had also been cut off.

Peter J. Tyldesley, a solicitor and consultant for the Law Commission, said that a vital part of national history had been lost. In its original condition, the document would be likely to raise a high five-figure sum at auction. “There are sections which are completely destroyed, sections where the entire text block has disappeared into a smeary mess,” Mr Tyldesley said...

He told The Times: “I thought the British Library was the safest place for it. How wrong I was.”

Within the manuscript, Thomas Tyldesley (1657-1715)...detailed everyday life and political events, as well as the plotting and the intrigue with which his family was involved in their pursuit of the Jacobite cause...

The British Library told The Times that the diary had “suffered accidental damage”, but insisted that it was an “isolated incident”. Helen Shenton, the library’s head of collection care, said: “The book had been kept in safe storage in a protective box and it was not until the book was opened that the stains were discovered.”