Asking to remain anonymous, the collector said that he had made the decision as news emerged yesterday that the college was negotiating an pounds 11m offer for the painting and that on Monday the college council will be asked to vote on whether to accept the price.
He said: 'I will change my will. This is not for negotiation.' If he does, Royal Holloway will not receive a collection 'covering hundreds of feet of shelving' of antiquarian books and musical manuscripts dating from the 15th to the 19th centuries.
The college, which is seeking to raise up to pounds 20m for the upkeep of its main building, was allowed by the Charity Commissioners to proceed with the sale of Turner's Van Tromp going about to please his Masters, Ships at Sea, getting a good wetting, 1844. A Constable and a Gainsborough are also on its hit-list. Royal Holloway has argued that these paintings 'are not part of the core high Victorian art that forms the collection'.
Appeals to the Attorney General and the Parliamentary Ombudsman failed to stop the sale, although campaigners against it emphasise that the college is breaking the trust of the philanthropist Thomas Holloway, (1800- 83), who founded the college and gave it an art collection.
The antiquarian collector believes that if the terms of a donation or bequest can be overturned, other benefactors will think twice about leaving their collections to public or semi-public institutions.
The concern was echoed by Graham Greene, chairman of the Museums and Galleries Commission: 'If people accept gifts, they ought to abide by the terms by which the gift is made . . . overturning the benefactor's wishes will deter future donors. It's hardly supporting the Government's policy of encouraging more private giving.'
In the event of a sale, the painting may well leave Britain. Although such a work is likely to receive an automatic export stop to allow a British buyer to match the price, one source said the procedure would 'mark time for six months and then the painting will go. Who's going to raise pounds 11m here?' No one from the college was available for comment.