You wouldn't be at all shocked to find Colonel Mustard brandishing a candlestick in the library at Great Brampton House - though he would be coveting rather than killing. This classic country house and its quintessentially English contents are all up for sale and are expected to fetch a total of £5 million. “It's probably the country house sale of the decade,” says Harvey Cammell, director of Bonhams and the man given the task of cataloguing the contents. “It's not just a home - Lady Pamela Pidgeon ran it as Britain's only ‘antiques mansion' for nearly 30 years. It's packed with things.”

Famous clients included Ava Gardner, Luciano Pavarotti and Lord Heseltine - famously mocked by Alan Clark as a man who “had to buy his own furniture”. A signed photo of Gary Barlow, the Take That singer, hanging in Lady Pidgeon's study reads: “To Lady PP - Can't wait for another mind-blowing afternoon.” From far and wide they came to her Regency house in the tiny village of Madley, near Hereford, to buy into her dream of classic English country-house style. Knowing that her clients craved exclusivity, she had them collected by a chauffeur-driven Rolls-Royce or Bentley (both for sale). The ultraexclusive used the household helipad.

“It's an eclectic, flamboyant mix,” says Cammell. “She knew her clients and their needs very well. She was an avid collector of paintings, furniture and Asian ceramics but she was a businesswoman too. She lived and worked here and everything is for sale, from tea cups worth £10 to six-figure pieces of museum-quality furniture.”

Lady Pidgeon was born in Somerset. She went to Malaysia with Major Francis Howells, her first husband, where her mother sent her the interiors magazines that sparked her love of antiques. On returning to England she began selling antiques from the back of her Morris Traveller - her only possession not for sale. After her husband's death in 1987 she married the property developer Sir John Pidgeon. Business blossomed and shebegan placing her idiosyncratic adverts in Country Life magazine.

“They were always flamboyant,” says Cammell, “and she was always wearing three strings of pearls.” Some snobs sniffed but Lady Pidgeon prospered. She sold a Canaletto for more than £2million.

“She's sad about selling up,” says Rose Powell, her housekeeper for 29 years. “But she's moving to Australia with Sir John and she can't take it all with her. To some clients she was Pamela, to staff she was Lady Pidgeon, to me she was LP. I am not sure what I'll do now.”

There are 932 lots, priced from £30 to £250,000. “Most items have no reserve because they're priced to go,” Cammell says. “It's a very special sale - our biggest off-site since the Savoy. We expect to make £1.5-£2million.”

The house is divided into homely living quarters and glamorous, themed showrooms that include the Green Room, Wedgwood Room and Breakfast Room. Star lots are in the the Russian Drawing Room. Twin portraits by Alexander Roslin of Grand Duke Paul Petrovich of Russia (later Tsar Paul I) and his wife, Maria Fyodorovna, hang in fine giltwood frames decorated with the imperial crest. Russian expatriates aresaid to be clamouring. A 17thcentury Neapolitan cabinet that once stood at Chequers is the most expensive lot, starting at £150,000.

“That was LP's favourite thing,” Powell says, pointing to another, very unshowy, cupboard standing in the corner. “It was the first thing she bought and the only thing she would never sell. Till now.”

The most curious lot hangs at the foot of the grand staircase. The portrait of Anne, Marchioness of Donegal, was painted by Francis Cotes. Soon afterwards the great lady changed her hairdo so she ordered Thomas Gainsborough to redo her head. It's on at £40,000 to £60,000. That's the lots. The house, which is set in 11 acres, is on with the local agent Bill Jackson: “It's a handsome house, not expensive at £2million because we've followed the market down. It could be a home, an hotel or, I suppose, another antiques place. We've had lots of American interest.”

The ten-bedroom house was reduced from three storeys to two in the 1950s so has some curious stairs leading nowhere. The cellars suggest a more ancient dwelling. It all needs updating. Outbuildings include the garages used by Lady P's chauffeurs. “I'll still be living on the grounds,” Powell says. Sadly for the new owner, she's not included in the sale.

The Great Brampton House sale is on Wednesday, October 1. Preview days: September 27-30. bonhams.com, 0870 0273602; billjacksoninternational.com , 01432 344779

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