The future of one of the most important historic houses in Britain is under threat unless the National Trust can raise the funds to save it.

Seaton Delaval Hall near Blyth in Northumberland was built between 1718 and 1731 by Sir John Vanbrugh (1664–1726), architect of Blenheim Palace and Castle Howard, as well as a leading dramatist and wit of his day.

With its bold, daring and dramatic architectural style, it is widely regarded as the greatest masterpiece of the English Baroque.

Yet it could now be turned into a hotel or a golf club, or some other commercial development unless the National Trust can raise around £13 million to save it for the nation.

Its owner, Lord Hastings, is having to sell the Hall, along with its gardens, grounds and a large area of the surrounding countryside, following the death of his parents last year.

Although a Vanbrugh masterpiece would fetch far more than £13 million on the open market, he is giving the National Trust until the end of the year to acquire it.

He said: “My father spent many years restoring Seaton Delaval Hall and its gardens and putting together the collection within the House. He was very supportive of public access to the land and coast owned by the Estate.

“I am very keen to see his vision continued and to safeguard the future of the house. Therefore I would like to give the National Trust every opportunity to acquire the property.”

The heritage body, which was set up to protect historic buildings in England, Wales and Northern Ireland, is so alarmed for the house’s future that it has taken the dramatic step of launching both a fundraising appeal and a major consultation.

The Trust frequently consults with relevant communities and interest groups on its activities. But never before has it done so on such a scale on a major property acquisition. Through questionnaires and other activities, schools and local communities will be involved in deciding the future of one of the great architectural feats of the 18th century. A major cultural centre is one proposal.

The National Trust will invest £6.9 million from its own resources in an endowment to look after the house and surrounding parkland in perpetuity. However, it needs a further £6 million.

Fiona Reynolds, Director-General of the Trust, said: “If it is sold, any number of things could happen to it... It is incredibly untouched by modern intrusion. That would be impossible to retain with any conversion, whether a hotel, a golf course or a private residence.”

Estimating its value on the open market, she said: “What is it worth? It’s a Vanbrugh masterpiece.”

Although part of the Hall’s interior is a romantic ruin, having been badly damaged by a fire of 1822, the rest retains Vanbrugh’s original design brilliance, including the magnificent stonework, sculptures, fireplaces and spiral staircase. The entrance hall is one of the greatest rooms in Western Europe. The exterior is intact - a perfect example of English baroque at its finest.

Delaval Astley, the 23rd Lord Hastings, 48, a farmer and businessman, became its owner when he succeeded to the family title following the deaths of his parents. Edward Delaval Henry Astley, the 22nd Lord Hastings, died last year, at the age of 95, followed by his wife Nicki eight months later. They had lived in the house’s West Wing, opening the rest of the building to the public twice a week during the summer.

The Hall stands on an estate which has been owned by the Delaval-Hastings family since the time of the Norman conquest of the north of England around 1080. It was built for George Delaval, the English naval admiral and diplomat, who fell from his horse and died before the hall was completed.

The Delavals were a well known local family who made their fortune in coal in the 17th century and later in glass production.

Carol Pyrah of English Heritage said: “Seaton Delaval Hall is without question an outstanding historic house.”

To make a donation, visit www.nationaltrust.org.uk/seatondelaval or call 0844 800 1895

Editor's choice

• Burning Bush with W
• Revolution at the new Saatchi Gallery
• Boy George on sex, drugs and Amy Winehouse