Wentworth Woodhouse, near Rotherham, is twice as wide as Buckingham Palace and formerly owned by the aristocrat who inspired Jane Austen’s Mr Darcy.
It boasts five miles of corridors, is 150 times the size of your average home and has an estimated 365 rooms – but is so vast nobody knows the exact number.
Crispin Holborow, director of Savills’ country department, is the man tasked with finding a buyer for the mansion he describes as a ‘once in a generation sale’.
He said: “Homes with this level of history and grandeur don’t come up for sale. I’ve not sold a bigger house and I am not sure there is one.”
The stately home sits in 82 acres of gardens and woodland, surrounded by the even larger Fitzwilliam Estate.
The house itself covers 2.5 acres – nearly one-and-a-half football pitches – while the front of the house is 606ft wide, making it the longest country house facade in Europe.
Even those who can afford the asked price need to stump up more cash to cover repair costs.
Surveys into repair work have found £42 million is needed to be spent on the house over the next 12 to 15 years to meet the backlog of repairs and subsidence damage.
The stately home was bought by architect Clifford Newbold, who fell in love with the property and bought it for little over £1.5million in 1999.
He worked tirelessly to restore it to its former glory after spotting the house in a newspaper advert and falling in love with it.
Mr Newbold poured his heart and soul into the building and would get up at 8am each day, working with teams of historians, conservationists and architects, to draw up a Conservation Management Plan.
Last year, Save Britain’s Heritage and its partners formed the Wentworth Woodhouse Preservation Trust to take over the house in agreement with its current owners to try to raise the funds needed for the repair work to go ahead.
But Mr Newbold died peacefully in his sleep last month, aged 89 and his family have now decided to sell the home.
The Newbold family said: “Having made the reluctant decision to sell, it was always the plan to bring Wentworth Woodhouse to the market in the spring of 2015.
“It is the family’s greatest wish to find someone to carry on our work and see the house in safe hands and secure for the long term.
“Various discussions have taken place over the last couple of years with SAVE, while they have tried to gain support for a charitable trust to take it over.
“It has not been as easy as everyone hoped to raise the necessary funding and thus we are continuing to look for an individual or organisation to whom we can pass on the baton of stewardship for future generations to enjoy.”