LONDON-This time it was the bidding that made people gasp.Banksy, the world’s most famous street artist, joined the ranks of the world’s most expensive artists Thursday night when his 2009 satirical painting, “Devolved Parliament,” showing Britain’s House of Commons populated by chimpanzees, sold for 9.9 million pounds with fees, or about $12.1 million, at Sotheby’s, setting an auction high for his work.

“This is like the moment Basquiat made it into the Soho galleries in the 1980s,” Alex Branczik, Sotheby’s head of contemporary art in Europe, said after the sale. “I’ve realized he’s a serious artist, but he has such a broad popular base. He appeals to established and new collectors,” added Mr. Branczik.

“Devolved Parliament,” a Victorian-style oil on canvas showing the debating chamber of the House of Commons packed with earnest-looking chimps, was being offered at the evening auction of contemporary art just four weeks before a Brexit-traumatized Britain is due to leave the European Union. Signed and dated 2009, the painting, offered by a private collector, had been estimated to sell for between £1.5 million and £2 million, or $1.9 million to $2.5 million.

Acoris Andipa, a London dealer who specializes in Banksy, called the 14-foot-wide “Devolved Parliament” “an important piece,” saying it was the most valuable work executed solely by Banksy to have so far appeared at auction. (Other pieces have sold privately for at least $3 million.) “It’s just so topical. And the sale was perfectly timed for Frieze,” Mr. Andipa added, referring to the contemporary art fair currently running in Regent’s Park that always draws international collectors.

But for some in Sotheby’s packed salesroom, the result was an anticlimax. They had been hoping to witness a stunt as spectacular as the Banksy “shredding incident” that transfixed the world’s news and social media last October at Sotheby’s.

On this occasion, Banksy had already done his monkey business.

After a dramatic 13 minutes of competition, in which as many as 10 bidders were involved, at least five of them in the room, it was finally knocked down to a telephone buyer. At one point the hammer was poised to fall at £6.4 million, but a bidder at the back of the room flung up his hand at the last second, before finally giving way to the winning telephone bid.

“It’s a really important moment,” said Mike Snelle, half of the London-based artist duo, the Connor Brothers, who was in the salesroom. “The price was final recognition of how important an artist he is. The art world has taken time to catch up with how significant he is culturally.”