The National Galleries of Scotland could lose two of its greatest paintings after a decision by the Duke of Sutherland to sell the Old Masters, which have been on loan since 1945.

Unless the Galleries can raise £50million by the end of the year to purchase Titian's Diana & Actaeon, paintings from his collection, valued at more than £1billion, may be offered for sale on the open market. A second Titian, Diana & Callisto, has also been offered for sale to the Galleries in 2013 at £50million. An emergency grant of up to £20million has been requested from the Treasury - the first of its kind for more than 30 years - to help to buy the works.

The paintings have been offered at a discount to the nation by the duke. But the combined fee would be almost five times the record for a work of art acquired by a British public collection - set in 2004 when the National Gallery paid £22million for Raphael's Madonna of the Pinks. The decision to sell was described as a “defining moment in the Galleries' history” by John Leighton, their director-general.

He has agreed a unique partnership with the National Gallery in London in an attempt to raise the money. If successful, the paintings will be shared between London and Edinburgh.

The Times understands that Andy Burnham, the Culture Secretary, has asked the Treasury for an emergency grant of £10million to £20million to go alongside money raised by the National Heritage Memorial Fund and private donations.

The SNP government also indicated that it would be prepared to underwrite a share of the cost of a co-operative venture to save the collection, though no figure has been set.

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