Tracey Emin is due to deliver an artists' petition to Downing Street in a bid to save two paintings by the Renaissance master Titian for the nation.
The National Galleries of Scotland and London have until the end of December to raise £50 million to keep Diana And Actaeon in the UK, with the option of buying the second painting, Diana And Callisto, for a similar price in three years.
As part of the campaign to raise funds, a letter signed by luminaries including Lucien Freud, Damien Hirst and David Hockney will be handed to Downing Street, along with a reproduction of the work.