The painting is A Capriccio of the Scuola di San Marco - a late 1740s view of the great Renaissance building in Venice, brought to life by a variety of figures in conversation and at work. It had been estimated to sell for between pounds 1m and pounds 1.5m.
It was bought over the telephone by Hazlitt's, which had expected bidding to reach more than pounds 4m. John Morton Morris, its managing director, said: 'We were surprised to be able to buy it at that price.'
He insisted it had been bought for the gallery's stock. However, one leading dealer said that was unlikely in recessionary times: 'You wouldn't pay that much for stock. If you're buying a Canaletto to sell on for pounds 2m, you've got to sell it for pounds 3m. Otherwise there's no business in it. For dollars 5m, they (collectors) want a Venetian view. They don't want a Capriccio with washing on the line.'
But it is a matter of taste: at the other extreme, another dealer saw the pounds 2.2m as 'cheap' considering the work's quality.
Patrick Matthiesen, a leading dealer, said: 'It is unquestionably a good picture . . . The price is not outrageous . . . But if it was bought for stock, to resell, it is slightly expensive.'
About 86 per cent of the first part of the auction found buyers. Among other high prices were Michiel van Musscher's 1672 Notary in his Office, which made pounds 287,500 against a presale estimate of pounds 100,000 to pounds 150,000.
Opinion was also divided over the success of the sale. One dealer felt that confidence was returning to the market - particularly as there were buyers for works by lesser masters, even religious subjects, often considered 'difficult'. Another was less sure: 'It doesn't say anything about the market because the pictures are not very good.'
Mr Matthiesen said 'the most outrageous buy' was an image of Cleopatra catalogued as Italian school, circa 1660, which sold for pounds 170,000 to an anonymous buyer; it was estimated to make up to pounds 30,000. He believes that it is a later, possibly 19th-century work, judging from 'the overtly erotic pose that artists didn't use in the 17th century', the costumes and hairstyles.