ART / The Sitwell inheritance: The Sitwells - eccentrics, literati, rivals to the Bloomsbury set - but what did they actually do? Iain Gale examines their achievements

To Cyril Connolly they were 'a dazzling monument to the English scene'; to Noel Coward, 'two wiseacres and a cow'. The Sitwells, Edith and her brothers Osbert and Sacheverell, celebrated in an exhibition which opens in London on Thursday, dominated art and letters in the 1920s. However, through the entertainment value of their feud with the Bloomsbury set, and a temptation to dismiss them as decadent, jeunesse doree amateurs, their real achievements have been generally forgotten. While it was as poets and writers that they gained notoriety, it was by showing that there was an alternative to Bloomsbury and Impressionism, that the Sitwells left their mark on British art. As taste-makers and patrons, they inspired artists to look to their native traditions with a profound effect upon the development of 20th- century art.

Children of the eccentric Sir George Sitwell, the trio had an unconventional upbringing. Their desire to dominate the arts was inspired by a need to avenge themselves both upon their neglectful parents and the 'golden horde' of philistines who had shaped the Edwardian world.

Osbert took the first step in 1912, befriending Diaghilev, whose sensual Ballets Russes was the toast of London's chic avant-garde. By 1913, Edith too was in London, writing poetry from the squalid Bayswater flat where she entertained, among others, W B Yeats, T S Eliot and Ezra Pound. On leave from the trenches, Osbert dined at the Eiffel Tower restaurant with Wyndham Lewis and Augustus John. The Sitwells were quickly accepted into the Bloomsbury circle, and it was under the influence of the writings of Roger Fry and Clive Bell that the two brothers travelled to Paris in 1918 to gather material for the first of two proposed exhibitions of French and British contemporary art. The French show opened at Heals in August 1919, with the Sitwells' young friend Herbert Read manning the desk. It was a succes de scandale. Apart from showing new paintings by Picasso, Matisse, Derain, Vlaminck and Soutine, the brothers introduced London to the work of Modigliani. Conservative critics were outraged.

But the Sitwells were not conformist avant-gardists, and the Gordon Square circle would not have relished the second, unrealised exhibition, intended to introduce Paris to the work of the Vorticists - who had split acrimoniously with Bloomsbury in 1914. Naturally anti-naturalist, the Sitwells tired of the French-obsessed Bloomsburys and sought an art more suited to their own increasingly hedonistic sensibilities.

In 1920, Sacheverell commissioned Picasso to paint a series of murals at the family villa in Tuscany. When his father refused to pay, the commission passed to the Italian Futurist Gino Severini, who, like many artists after the Great War had adopted classical figuration. His approach, though, seen in the studies and photos of the murals shown here, was far less robust than Picasso's, with a Watteauesque wit and light- heartedness which suggest the direction in which Sitwellian taste was evolving.

Visiting Naples in 1920, Sacheverell had been overwhelmed by the exuberance of Baroque architecture. His excitement intensified after a visit, in 1921, to Lecce ('the Florence of Rococo art'). By 1922 he had completed Southern Baroque Art. At the time 'Baroque' was a term of abuse. But, published in 1924 the book sold out, creating in Kenneth Clark's words: 'a revolution in English taste . . . it was wonderful to find people so liberated from the accepted thought and values and particularly those of Bloomsbury and the domination of Roger Fry and all that muddy-coloured pseudo-classicism'.

Apparently unwittingly, Sacheverell had diverted English taste back towards the flaming line of Blake and Palmer, tapping into the natural English taste for the demotic and the romantically macabre, expressed in a tradition which continued through such Neo-Romantics as John Piper (commissioned by the Sitwells), to Bacon, Freud and Hockney. Bloomsbury austerity was replaced by Sitwellian flamboyance as Edith and Osbert also courted a shockable public with such extravagant performances as Facade, in which Edith's poems were set to music by their protege William Walton and spoken through a megaphone.

Visually, the dynamic medieval angularity of the Vorticists appealed to the trio's sense of a 'Plantagenet' past, while the precepts of Dada and Surrealism tempered their brand of safe champagne anarchism. Flaunting the mantel of Whistlerian aestheticism driven underground by the Wilde scandal, they influenced undergraduate circles at Oxford which included Evelyn Waugh, John Betjeman, Harold Acton and Kenneth Clark.

The transformation was captured by Waugh in Brideshead Revisited in Charles Ryder's 'conversion' from Clive Bell's 'significant form' - an aesthetic realised by rational debate - to an instinctive understanding of beauty. Among artists, the urge was exemplified by the work of Cecil Beaton and Rex Whistler, who made his name with the eloquently Baroque Tate Gallery restaurant murals of 1927 and, in 1928, painted Edith as an androgynous mock-Pope, seated on a huge Rococo cartouche of a throne. Osbert Lancaster gave the style its lasting title: 'Curzon Street Baroque'.

While the style engendered by Sacheverell might at times appear precious, and the holes in his scholarship amuse modern historians, without his groundwork British artists might never have rediscovered those extremes of decoration which are one of the most enduring characteristics of this country's heritage.

National Portrait Gallery, from Thursday to 22 Jan

(Photograph omitted)