He said the Tate would soon be negotiating-with Mr D'Offay on the final price of the collection and working out the gift-purchase component.
Mr D'Offay started his artistic dabblings when he was a student after buying the books and papers of two obscure poets and then selling them at a profit.
One of his first customers in the art world was Paul McCartney, who in 1965 acquired a 1927 Jean Cocteau drawing. Not long afterwards Mr D'Offay became the most powerful art dealer in London.
Together with his wife, former Tate curator Anne Seymour, Mr D'Offay staged exhibitions by modern artists that rivalled any major public museum.
But towards the end of his fourdecade career in the art world, some critics said he was losing his touch. Mr D'Offay lost Gilbert and George as clients in 2000 to Jay Jopling at White Cube; the maverick pair described their former agent as "a f***ing c**t" more interested in money than art.
However, Evening Standard art critic Brian Sewell commented upon his retirement in 2001: "The sudden loss of Anthony d'Offay's energies is a more serious blow than we can estimate."
Anna Somers Cocks, former editor of the Art Newspaper, said: "He is not like Jay Jopling, who goes out and finds people, but he has always been very good at picking artists just as they come into their reputation."