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The buyer, Russian metals and mining magnate Alisher Usmanov (who in the same week took his stake in Arsenal Football Club to 15 per cent) intends to take the collection to Russia.

The move is not unprecedented for a sale of Russian works of art. In a similar pre-emptive deal, Victor Vekselberg, an oils and metals tycoon, paid close to £50m to acquire the Forbes collection of Fabergé just days before it was scheduled to sell at Sotheby’s New York in 2004.

Sotheby’s dubbed the Rostropovich-Vishnevskaya Collection one of the most important collections of Russian art in private hands. It includes 22 paintings by the portraitist Ilya Repen and an important post-Revolutionary work by Boris Grigoriev, his Faces of Russia from c.1918.

Mstislav Rostropovich, the celebrated cellist and conductor, who died in April this year, assembled the collection while living in exile in Britain and France after fleeing the Soviet Union in 1974.

The Mr Usmanov price paid was not disclosed but was described as substantially higher than the £20m top estimate.

If, as widely reported, the move was designed to curry favour with the Putin regime, then it appears to have had its desired effect.

• In the same week Sotheby’s also announced the private treaty sale of another piece that would have been a highlight of their autumn season in Hong Kong. A Qianlong period Imperial bronze horse’s head from the zodiac fountain of the Summer Palace in Peking which was due to go under the hammer on October 9 has been purchased by Dr Stanley Ho in a sale brokered by Sotheby’s for HK$69.1m (£4.42m), a record price for Chinese Qing sculpture.

Dr Ho, Standing Committee Member of the National Committee of the Chinese People’s Political Consultative Conference, has decided to donate the bronze to China, and an agreement was reached with the consignor through Sotheby’s Hong Kong.