It was one of Mr. Macquisten’s reporters who found out what little was known about the buyer.

With China’s wealth rapidly rising, mainland Chinese buyers have been a major force in pushing up the prices of Chinese antiquities, reversing, at least in small measure, the flow of Chinese artworks to the West during the centuries before the Communist revolution in 1949  and the loss of imperial treasures when the Chinese nationalists fled the Communist victory for Taiwan, taking huge quantities of antiquities with them.

The vase’s price exceeded the record for Chinese antiquities set just last month in Hong Kong, when another Qianlong vase sold for $34.2 million.

For Bainbridge’s, the sale price of the vase represented a huge leap, putting the auction house, at least momentarily, in a league with the blue-ribbon art houses like Sotheby’s and Christie’s, where sales running into the tens of millions of dollars have become almost routine in recent decades. Bainbridge’s biggest sale before Thursday was $160,000 for a Ming enamel piece it sold two years ago.

The sale was held in the London suburb of Ruislip, neighboring Pinner, where the vase was found. Pinner is best known in modern times as the place where the singers Elton John and Simon Le Bon went to school.

As the auction house was trying to establish a selling price, Ms. Porter said, the vase had been taken for viewing at the Arts Club in London, where it was deposited for some time on a “metal table next to the kitchen.”

The auction house itself began to realize its rarity only when a consultant on Chinese ceramics, Luan Grocholski, was called in to evaluate it. “Luan took a long, hard look at it and could hardly believe his eyes,” Ms. Porter said.

Still, Bainbridge’s had set its presale estimate between $1.3 million and $2 million.

“We are absolutely stunned,” Ms. Porter said after the auction. “This must be one of the most important Chinese vases to be offered for sale this century. How it reached Ruislip is something we will never know, and that it is in such fine condition is amazing.

“We’re just a very typical local auction house, so as you can imagine it was something of a surprise.”