He was born in 1910, his father having served in the Indian Civil Service and his uncle Sir Lewis Casson the actor and producer and husband of Sybil Thorndike. As a child, while his father was at the School of Navigation, he grew up among ships and wharfs and watched the great liners pass down the breezy expanses of Southampton Water. At boarding school, at Eastbourne College, like most drop-outs from organised games he took refuge in reading (he had a remarkable memory for quotations) and of course drawing, but it was not until Cambridge that he turned from the Classics to architecture and learnt at the tiny School of Architecture to draw in perspective with a fountain pen and never to use an indiarubber.
The 1986 show had a sketch of himself (all his life he drew himself with affectionate irony) as the tiny cox of his college boat receiving a medal from the enormous Mrs Stanley Baldwin "in a hat like an abandoned allotment". At weekends he haunted the Festival Theatre, painting scenery and meeting the resident celebrities.
His teachers both at St John's College, Cambridge and later in London at the Bartlett School at University College were eminently traditional, and his first little steep-roofed house, on which he always looked back with affection, might have been the work of Edward Maufe. But there was one exception - his year master at Cambridge, Christopher Nicholson, a modernist of great promise who was to be Casson's friend and first partner from 1937 until his death in 1948 in a gliding accident at Dunstable.
It was at the Bartlett that he met Margaret Troup from South Africa, known to her friends as Reta and to him alone as Moggie, who was soon to be his equally talented wife. But building jobs were scarce in the late Thirties and he turned to journalism as a columnist on the Architects' Journal and on Graham Greene's short-lived Night and Day.
In 1939, with the outbreak of war, he characteristically enlisted in the River Thames Fire Service before moving to camouflage, and in 1944 found himself, cast against type, in the Research Department of the Ministry of Town and Country Planning under William Holford.
He continued writing. As he said later, "It was, I suspect, my journalism and illustrations rather than my few bits of unmemorable architecture that were the cause of the invitation in 1948 to join Gerald Barry's team being set up to plan the Festival of Britain. It proved to be three years of almost total elation."
Much has been written about the 1951 Exhibition: unquestionably it was the "tonic" that the shabby and exhausted nation desperately needed, and as Director of Architecture Hugh Casson deservedly received a knighthood. Neville Conder had joined Casson's practice after the war and in 1952 they won a limited competition for a master plan for the development of the Arts Faculty site at Cambridge. When in due course they were commissioned for the first group of buildings the Casson Conder Partnership came into being. Thirty years later, when the development was completed, Conder was to write a masterly essay on the methodology of such long-term enterprises.
Post-war architects often practised in pairs (later the fashion for mysterious initials took over) which led to much discussion among critics and historians, accustomed to the tradition of the single artist, about who really did the designing. The crude assumption was that the first was the sociable job-getter, the second the creative recluse. Architects know that in fact it's all done by talk over the drawing-board and resent such sleuth-work.
In the case of Casson Conder it would be particularly invidious because of the unity-in-diversity of their work (from large office buildings to telephone kiosks to ship interiors) and the loving attention given to the tiniest projects. Casson would say that his favourite among their buildings was the 1965 Elephant House at the London Zoo, though that rough beast is uncharacteristic. Others may feel that the first buildings at Cambridge have worn remarkably well and may resent the deliberately contemptuous intrusion of Stirling's Library.
Their three large office buildings - in King Street, Manchester and Fetter Lane and Charing Cross in London - are among the best in that unloved hand, and their more recent Anglo-Islamic Ismaili Centre opposite the Victoria and Albert Museum in London has great charm. What characterises all their work is elegance, lightness of touch and sensitivity to surroundings (all of which qualities were later to go out of fashion).
Several of the architects and designers involved in the South Bank Exhibition were invited by Sir Robin Darwin to become senior staff of the reconstituted Royal College of Art, where in 1953 Hugh Casson was put in charge of a new School of Interior (later Environmental) Design with Reta as Senior Tutor. Darwin had hoped for a School of Architecture, but was told that, with architecture in its historic sense still, in John Summerson's words, "an illegal profession", there were too many already. But a school of architecture, over the years until Casson's retirement in 1975, it gradually became.
Meanwhile his "etcetera" activities spread in a happy variety of directions. He was a born Londoner, traversing it in his tiny Mini and drawing buildings with the same affection with which Edward Ardizzone drew people, and only rarely escaping with his family to a windswept coastguard's dwelling facing the Solent and the Isle of Wight. His childhood love of the sea and nostalgia for the Royal Navy found expression in the designs for the royal apartments in HMY Britannia, when he found an enthusiastic client in Prince Philip. Later, through Sir Colin Anderson's connection with the RCA, the firm was to design all the public rooms in the new P&O flagship Canberra.
Then his family connections and Cambridge addiction to the theatre gave him the chance to design sets for Glyndebourne and Covent Garden. Planning consultancies followed for historic Wessex city centres (Bath, Bristol, Salisbury, Chichester) with the mixed results of such efforts in the face of traffic and tourism. Twenty-three years on the Royal Fine Art Commission (1960-83) were accompanied by a daunting profusion of other appointments and committees. Casson claimed to believe that committee work was "an art form in its own right" and was bad at saying No.
Finally, in 1975, came the Presidency of the Royal Academy - the first architect since Sir Edwin Lutyens in 1938 to undertake it. Painter academicians are tempted to give architect PRAs a rough ride, but over his nine years Casson emerged triumphant, achieving a dramatic improvement in the financial state, artistic "relevance" and public image of the Academy. The picturesque costume and unfailing wit with which he presided over annual dinners will not be forgotten by anyone who was there.
His illustrated Diary for 1980 is a vivid, part funny, part horrific account of one typical year among many through which his wife, amused and ironical, gave him heroic support, almost collapsing when they moved house in the middle of it: their three much-loved daughters came to the rescue. "I stood around moping; how one longs to be a handyman," he wrote, affecting a helplessness which belied his enormous energy and the core of steel that underlay his sense of fun. Hugh Casson's achievements were remarkable, but his personality outshone them.
Hugh Maxwell Casson, architect, artist and writer: born London 23 May 1910; senior partner, Casson, Conder & Partners 1946-76; Director of Architecture, Festival of Britain 1948-51; RDI 1951; Kt 1952; Professor of Environmental Design, Royal College of Art 1953-75, Provost 1980-86; RA 1970, PRA 1976- 84; KCVO 1978; CH 1985; married 1938 Margaret Troup (three daughters); died London 15 August 1999.