The boom in the art market has handed strong results to the two big auction houses, with Christie’s and Sotheby’s together selling about $7bn worth of artworks in the first six months of the year – 12 per cent more than last year.

Christie’s said on Thursday it had total worldwide sales of £1.8bn ($3.6bn), a rise of 10 per cent on the same period last year. That includes both auction sales and private treaty sales.