THE family of Graham Greene has launched an extraordinary public attack on the monopoly enjoyed by his official biographer, claiming that "censorship" is unfairly denying other writers access to the late author's personal papers.

Francis Greene, the author's son, and his niece, Amanda Saunders, have said that they are "shocked and unhappy" at the Professor Norman Sherry's stranglehold on the material. They are demanding that all the contents of the author's archives at Georgetown University, Washington, be opened to writers other than Prof Sherry.

The problem came to light when a Canadian academic who is writing a book on Edith Sitwell - with whom Greene had a long association - was told that he could not look at any of their letters. On his deathbed in 1991, Greene appointed Prof Sherry - a Professor of English at Trinity University, San Antonio - as his official biographer on the strength of two volumes on the writer that he had already published. More than 10 years on the third and fourth volumes by Prof Sherry on Greene have still not appeared.

At least three other academics with commissions from publishers have been told that they will have to wait until Prof Sherry has finished before they can look at Greene's archive. The author's family claim that Georgetown University Library is acting as gatekeeper for Prof Sherry in refusing to respond to the their requests for reasonable access to the papers.

According to the Greene estate, Nicholas B. Scheetz, the manuscripts librarian at Georgetown, has vowed that exclusive access to the material, acquired from Greene himself, will continue until Dr Sherry - a personal friend of Mr Scheetz - completes his work. The library claims that this is done at the late author's specific request.

The embargo has meant that even Francis Greene, who is literary executor to the author's estate, cannot publish a planned compilation of his father's journalism and literary criticism.

Francis Greene told The Telegraph that he was concerned at this "censorship", which "has given Sherry the monopoly of the archive". In a letter to the chief librarian at Georgetown University, Francis Greene disputes that his father ever granted exclusive access to the papers lodged there. "It is my conviction that no such request was ever expressed by my father . . . If you have evidence you should disclose it."

He adds that even if such instructions existed, it should not restrict writers engaged in research on other authors such as Sitwell or Evelyn Waugh. "To do so is a grave dereliction of your duty to scholarship and I cannot imagine on what such a policy could be defended." In another letter, Greene says: "It is a policy for which Graham himself would have expressed repugnance and ridicule."

Ms Saunders, his cousin, added that the situation was unacceptable. "It is contrary to Graham's whole spirit of sharing information with fellow writers and researchers," she said.

There has also been argument over 78 boxes of correspondence between Greene and his mistress, Catherine Walston, who inspired his novel, The End of the Affair. The library says that this material is not being restricted.

Prof Sherry's office said last week that he could not be contacted because he was ill. A spokeswoman said that he had "nothing to do" with access to the library. Both Mr Scheetz and Artemis Kirk, the University Librarian at Georgetown University, declined to comment. A spokeswoman for the university said that it had letters documenting Greene's request to restrict some of the archive for use only by Prof Sherry until his work was complete.

The spokeswoman added: "It is always Georgetown University Library's goal to support research and scholarship and we eagerly assist those who want access to our resources for these purposes. At the same time, we take our role as stewards of collections and gifts very seriously and are careful to balance open access with the responsibilities placed upon us in acquiring resources."