Litvinenko spy story could be acted out by Johnny Depp

His production company is to develop a book about the spy's death after Warner Brothers bought up the film rights to the as yet unpublished work, trade magazine Variety said.

Depp set up the company, Infinitum Nihil, in 2004 to work on projects he could be expected to be involved in, either as an actor or producer or both.

He is said to have been closely following the Litvinenko story and could now end up portraying the man himself on the silver screen.

The book will be called Sasha's Story: The Life and Death of a Russian Spy and is to be written by Alan Cowell, of the New York Times.

Cowell has followed the story since it broke last November when Litvinenko, 43, became seriously ill and was admitted to University College Hospital, London.

His health rapidly deteriorated as the world's media looked on before he eventually died on November 23. It later emerged he had been poisoned with polonium-210.

Speculation about Russia's involvement in his death deepened after the former KGB agent issued a statement from beyond the grave pointing the finger at president Vladimir Putin.

The Kremlin has always denied being involved and an ongoing international investigation has led police to Russia, Italy and Germany.

Cowell will document Mr Litvinenko's life and poisoning, as well as talk about the implications of the case on nuclear proliferation and international terrorism, Variety claimed.

He is due to take leave from work to write the book, which is due out later this year and has already been sold in advance to publishers in France, Holland and Denmark.