One of the three parts of the triptych showing John Edwards

The works show Edwards, who was a barman when he met Bacon in 1972, sitting on a stool in an empty studio space from three different perspectives.

Jussi Pylkkanen, Christie's international director, said: "It is a piece that Bacon himself identified as being of museum quality."

Finest works

The paintings were done in the 80s and Bacon's triptychs are widely recognised as being his finest works.

Bacon was one of the last century's most commercially successful artists, earning about �14m from his paintings before his death.

He dealt with themes of death and decay and his style has often been described as existentialist.

The artist once said: "I don't know that I should talk about a triptych in my case.

"Of course, there are three canvases, and you can link that to a long-standing tradition. The primitives often used the triptych format, but as far as my work is concerned, a triptych corresponds more to the idea of a succession of images on film."

Also sold at the auction of post-war art was Gerhard Richter's Venice (Steps), which attracted very competitive bidding and eventually went for �938,750.

Antonio Saura's Triptico (Crucifixi�n) sold for a record price of �487,750, while Yves Klein's MG 20 sold for �465,750, more than four times pre-sale expectations.