After coming under the influence of the art experts Bernard Berenson and Roger Fry, Clark was appointed director of the Ashmolean Museum in Oxford aged twenty-seven, and three years later he was put in charge of Britain's National Gallery.

During the Second World War, when the collection was moved from London for safe keeping, Clark made the building available for a series of daily concerts which proved a celebrated morale booster during the Blitz.

After the war, and three years as Slade Professor of Fine Art at Oxford, Clark surprised many by accepting the chairmanship of the UK's first commercial television network.

[13] The school library contained the collected writings of John Ruskin, which Clark read avidly, and which influenced him for the rest of his life, not only in their artistic judgments but in their progressive political and social beliefs.

[2] While at Oxford, Clark was greatly impressed by the lectures of Roger Fry, the influential art critic who staged the first Post-Impressionism exhibitions in Britain.

[20] It was greeted with public and critical acclaim, and raised Clark's profile, but he came to regret the propaganda value derived from the exhibition by the Italian dictator Benito Mussolini who had been instrumental in making so many sought-after paintings available.

[21] Several senior figures in the British art world disapproved of the exhibition; Bell was among them, but nevertheless he continued to regard Clark as his favoured successor at the Ashmolean.

In an editorial, The Burlington Magazine said, "Clark put all his insight and imagination into making the National Gallery a more sympathetic place in which the visitor could enjoy a great collection of European paintings".

[37] He had rooms re-hung and frames improved; by 1935 he had achieved the installation of a laboratory and introduced electric lighting, which made evening opening possible for the first time.

[37][n 6] In several years he had the gallery opened two hours earlier than usual on the day of the FA Cup Final, for the benefit of people coming to London for the match.

[43] Other important acquisitions, listed by Piper, were Rubens's Watering Place, Constable's Hadleigh Castle, Rembrandt's Saskia as Flora, and Poussin's The Adoration of the Golden Calf.

[44] The British press protested at the waste of taxpayers' money, Clark's reputation suffered a considerable blow, and his relations with his professional team, already uneasy, were further strained.

One suggestion was to send them to Canada for safekeeping, but by this time the war had started and Clark was worried about the possibility of submarine attacks on the ships taking the collection across the Atlantic; he was not displeased when the prime minister, Winston Churchill, vetoed the idea: "Hide them in caves and cellars, but not one picture shall leave this island.

[52] Although the pictures were in storage, Clark kept the National Gallery open to the public during the war, hosting a celebrated series of lunchtime and early evening concerts.

For the gallery he wrote a slim volume about Constable's The Hay Wain (1944); from a lecture he gave in 1944 he published a short treatise on Leon Battista Alberti's On Painting (1944).

[62] Clark served on numerous official committees during this period,[n 10] and helped to stage a ground-breaking exhibition in Paris of works by his friend and protégé Henry Moore.

He admired Giles Gilbert Scott, Maxwell Fry, Frank Lloyd Wright, Alvar Aalto and others, but found many contemporary buildings mediocre.

Many of those opposed to the new broadcaster feared vulgarisation on the lines of American television,[66] and although Clark's appointment reassured some, others thought his acceptance of the post a betrayal of artistic and intellectual standards.

He had appeared on air frequently from 1936, when he gave a radio talk on an exhibition of Chinese Art at Burlington House; the following year he made his television debut, presenting Florentine paintings from the National Gallery.

[70] Both he and television were finding their way, and programmes in the series ranged from the stiff and studio-bound to a film in which Clark and Henry Moore toured the British Museum at night, flashing their torches at the exhibits.

[79] The series consisted of thirteen programmes, each fifty minutes long, written and presented by Clark, covering western European civilisation from the end of the Dark Ages to the early twentieth century.

There were complaints, then and later, that by focusing on a traditional choice of the great artists over the centuries – all of them male – Clark had neglected women and presented "a saga of noble names and sublime objects with little regard for the shaping forces of economics or practical politics".

[86] He commented that his outlook was "nothing striking, nothing original, nothing that could not have been written by an ordinary harmless bourgeois of the later nineteenth century":[87] I hold a number of beliefs that have been repudiated by the liveliest intellects of our time.

[86]The broadcaster Huw Wheldon believed that Civilisation was "a truly great series, a major work ... the first magnum opus attempted and realised in terms of TV.

[84] The British Film Institute notes how Civilisation changed the shape of cultural television, setting the standard for later documentary series, from Alastair Cooke's America (1972) and Jacob Bronowski's The Ascent of Man (1973) to the present day.

The National Gallery observes about this series, "These art history lectures are an authoritative study of Rembrandt and feature examples of his work from over fifty museums".

He was known throughout his life for his impenetrable façade and enigmatic character, which were reflected in the two autobiographical books: Piper describes them as "elegantly and subtly polished, at times very moving, often very funny [but] somewhat distanced, as if about someone else.

[101] The twin daughter, Colette, became an official and board member of the Royal Opera House; she outlived her parents and brothers, and was the key source for James Stourton's authorised biography of her father, published in 2016.

[102] During the Second World War the Clarks lived at Capo Di Monte, a cottage in Hampstead, before moving to the much larger Upper Terrace House nearby.

[118] Clark knew that his broadly traditional view of art would be anathema to the Marxist element in the artistic world, and was unsurprised when he was attacked by younger critics, notably John Berger, in the 1970s.