A major portrait by Irish artist Sir William Orpen sold for over €1.1 million at a Sotheby's art auction in London yesterday.

‘Portrait of Lady Idina Wallace’ was bought by an unnamed private bidder in the United States for £ 962,500 (€ 1,147, 492).

The price was at the low end of the estimate (£ 800,000-£ 1.2 million/€ 940,000- €1.4 million).

The painting is one of a series of portraits of aristocratic women made by the artist in London before the first World War. Orpen was paid the then exorbitant fee of £750 for the commission.

Lady Idina Wallace (1893-1955) was immortalised as "The Bolter" by novelist Nancy Mitford and was later a central figure in British colonial society in Kenya.

The price is the second highest paid for a painting by Orpen who was born in Stillorgan, Co Dublin in 1878 and died in London, in 1931.

In 2001, Sotheby’s sold his ‘ Portrait Of Gardenia St George With Riding Crop’ for £ 1.9million (€ 2.24 million) – also to an anonymous American collector.

Yesterday’s sale at Sotheby’s was the first of three auctions in London this week featuring Irish art.

Prices for Irish art have dropped sharply since the boom and yesterday only half the Irish paintings in the auction of British and Irish art found buyers.

A selection of sketches by Orpen failed to sell except for one: a pen and ink drawing of an unhappy artist at his easel painting a landscape titled “Portrait of a Young Man Trying The Impossible in Dublin: Dublin At Sunset” which sold for £ 10,000.

More paintings by Irish artists go under the hammer in London today at Bonhams and tomorrow at Christie’s.