One of the UK�s leading independent art charities has thrown its weight behind the 11th hour campaign to secure the future of a national treasure.

One of the UK's leading independent art charities has thrown its weight behind the 11th hour campaign to secure the future of a national treasure.

The Art Fund has agreed to underwrite the acquisition of Dumfries House, after the Marquis of Bute announced plans to sell off one of his family's ancestral homes.

The house near Cumnock in Ayrshire and its unique collection of furniture and antiques are to be sold this summer and generate almost £20m, prompting a campaign by SAVE Britain's Heritage, one of the country's most influential conservation groups, to secure it for the nation.

The house contents include one of the world's finest collections of Thomas Chippendale furniture and many items are expected to fetch record-breaking sums. Now the Art Fund has made the biggest pledge since it was formed in 1903, to underwrite the purchase of the house and its contents up to a total of £2m.

The Monument Trust, one of the Sainsbury Family Charitable Trusts, pledged £4m to the campaign on Tuesday and a day earlier, the Garfield Weston Foundation pledged £1m.

It brings the total on the table to £7m representing a quarter of at least £25m thought to be needed to buy up the house and contents for the nation.

SAVE Britain's Heritage, which is seeking Scottish Executive support, has prepared a plan for placing the house in the control of an independent trust which will open the house to the public as a tourist attraction.

The group says that if the campaign fails the house will be sold and its contents will be auctioned separately in July.