The lawyers claim that the artist would have wanted them destroyed because he always denied making such preparatory sketches, and that the neighbour, Barry Joule, was "in blatant breach of Bacon's trust" by preserving them.
Despite the criticisms made of him, the row lends support to Mr Joule's claim that the works are by Bacon. Last year the Tate Gallery in London refused to display the collection, rejecting its authenticity. David Sylvester, a leading Bacon expert and Tate adviser, disputed its provenance.
John Edwards, Bacon's former companion, inherited the bulk of the estate. Mr Joule, Bacon's neighbour for many years until the artist's death in 1992, believed the works were given to him as a present.
"Francis was always very categoric. If he wanted something destroyed, he was very straightforward about it. Over the years I destroyed many paintings for him that he didn't want kept." But on this occasion, Bacon said: "You know what to do with it." Mr Joule said he had understood that the works were his to do what he wanted with them. He added: "If they claim that it was Francis's wishes to destroy them, are they going to destroy them? Certain scholars are saying it's a very important archive."
Legal action permitting, the Irish Museum of Modern Art in Dublin intends to show parts of Barry Joule's collection in an exhibition early next year.
The estate's lawyers, solicitors Payne Hicks Beach, last week refused to discuss the claim on the material. Tony Shafrazi, the owner of the New York gallery now handling Bacon's works, did not return calls.
David Sylvester has said that many of the pages must have come from Bacon's studio because they included personal photos and material others could not have possessed. But he added: "I am among those who cannot see Bacon's hand in the rather banal brushstrokes and scratchings on these pages."
Yet Mr Joule believes his archive is as significant as the nearly 40 works - bought by the Tate for a rumoured six-figure sum last year - which go on display at the gallery this week.
He has his supporters. David Lee, the editor of Art Review magazine, said: "The interesting thing about the show coming up at the Tate is the opportunity it will present to compare the works they paid a lot of money for with the ones they rejected."
Both the Tate and Joule collections contain sketches which appear to relate to known paintings. This raises the prospect that Bacon deliberately misled biographers and interviewers by denying that he ever sketched for his large post-war oil paintings.
The first many people knew of any sketches was when four owned by the poet Sir Stephen Spender were shown at an exhibition in Paris in 1996. They, too, are to be shown in the Tate show.
But Dr Matthew Gale, curator of the exhibition, said: "When people asked Bacon in a direct way, he simply said he didn't make drawings or sketches."
The Tate's works were bought last year from Paul Danquah and Peter Pollock, friends of the artist in the 1950s and 1960s. The sketches seem to have been done quickly and show figures crawling, crouching and reclining. Dr Gale said it was unclear whether they were preparatory drawings for the giant oils or sketches carried out afterwards as a route to creating new works.
What seemed certain was that Bacon's post-war works were more carefully planned than had previously been thought.
Also acquired by the Tate were photographs and a book in which Bacon wrote lists apparently of potential subjects.
Dr Gale said: "That gives the impression to me, at least, that he is looking at his old paintings and thinking of reworking them for new paintings."
An art expert, who did not wish to be named, said the Joule material appeared very "puzzling and disturbing" and different from the Tate works. "All I would say (about the Joule archive) is it really does deserve significant inquiry rather than dismissal."
One of the possibilities to be explored, the expert said, was whether Bacon might have encouraged one of his lovers to experiment on art with him.Reuse content