The Art Fund has backed a £3.9m appeal by the Fitzwilliam Museum to buy a masterpiece by Nicolas Poussin.

The University of Cambridge’s principal museum has until the end of November this year to raise the sum to purchase ‘Extreme Unction’, valued at more than £14m, from the 11th Duke of Rutland’s 2000 Settlement.

The trustees of the Settlement have offered the artwork to the Fitzwilliam Museum in order to offset the inheritance tax incurred by its sale of another masterpiece by Poussin, ‘Ordination’, for £15m last year. Using the government’s acceptance-in-lieu scheme, the organisation can offset its tax by offering a work of importance to the nation. Because the tax bill is less than the value of the artwork, the museum is fundraising to make up the difference of £3.876m.

Last year, Art Fund increased its acquisition fund by 50 per cent, to £7m a year, in order to assist museums and galleries run fundraising campaigns to retain or buy artworks for the nation. This year has already seen galleries dipping into their reserves in order to secure masterpieces.

Ten per cent of the money needed to buy ‘Extreme Unction’ has already been pledged and the Museum has applied to the Heritage Lottery Fund for support. Supporters of the Fitzwilliam Museum have also been contacted to help fund the acquisition. The Art Fund will work with the Museum to apply to other funds and trusts.

Art Fund director Dr Stephen Deuchar described the cut-price offer of the artwork as an unique opportunity. “Even for a museum collection as fine as the Fitzwilliam’s, this great Poussin would be a transformative acquisition,” he said.

The Fitzwilliam Museum’s director Dr Timothy Potts said the painting would be a “uniquely rich” teaching resource and a major coup. “This would be the most significant old master painting acquired by the Museum for nearly a century and would transform our representation of French art and of the classical tradition,” he said. “It is a ‘destination painting’.”