Ison's favourite cities and buildings have survived better than he dared hope, not least due to his achievements as an architectural historian. Bath is still - as Ison declared in his introduction to The Georgian Buildings of Bath of 1948 - "beyond any question, the loveliest of English cities", and his classic book has been a cornerstone of its preservation.
Ison was born to a middle-class family in Leamington. He worked as a junior assistant in the office of Frank Verity, the theatre architects, and studied architecture in the evenings. These early years at the drawing board were fundamental to his merit as a historian: he was unusually attentive to the visual subtleties of a building and his written descriptions were delineated with the precision of a draughtsman. The occasional verbal flourish was all the more delightful for its rarity.
Ison lived and breathed the language of classical architecture. In the last letter I received from him he pondered: "I wonder if Lutyens is the only English architect who has really made use of Sanmicheli." His heroes were the architects who played the Great Game of the classical tradition but also the 18th- century master-builders: the unknown men, such as Marmaduke Smith of Spitalfields or Thomas Jelly of Bath, who shaped our terraces and squares. Ison showed how they adapted the vocabulary of ancient temples to ceilings and stair balusters, window frames and doorknobs.
Ison continued to practise occasionally as an architect, and his principal patrons were Sir George and Sonia Binney, who valued his ability to capture a period style. At Horham Hill, near Thaxted, Essex, he designed a drawing room re-using some early-18th century panelling salvaged from London and a walled garden and swimming pool pavilions. He also designed the interiors of the townhouse in Eaton Row, Eaton Square, in the refined manner of Thomas Leverton's 1770s houses. Most notably, at Domaine des Vaux, St Laurence, Jersey he designed a formal garden in which a stepped amphiteatre faced a fountain garden. Ison also encouraged their son Marcus Binney, today President of Save Britain's Heritage, to study Sir Robert Taylor for his PhD.
In 1931 he married Leonora Payne, the artist and architect, whom he had met when they both worked in Verity's office. During the Second World War Ison worked in the highly secret model-making section of the RAF at Medmenham, Buckinghamshire, where his friend the distinguished calligrapher and artist Reynolds Stone stirred Ison's interest in Bath. Leonora also fell in love with the city and when, just after the war, she received a small legacy, they moved to Bath and bought a Regency house, No 5 Sion Hill Place. The legacy also enabled Ison to research The Georgian Buildings of Bath, which he published in 1948 and is still in print. His reputation in Bath is still infallible: well-thumbed copies of Walter Ison are as ubiquitous as Dr Spock in the city's middle-class households.
His next book was The Georgian Buildings of Bristol of 1952 and later he wrote English Architecture Through the Ages (1965) and English Church Architecture (1972) which became standard texts for the Oxford and Cambridge Schools Examination Board. All his books were beautifully illustrated by Leonora.
In the 1950s the Isons moved to London and restored an early-18th century house in Colebrook Row, Islington. Ison had come to work on the Spitalfields volume (1957) of the Survey of London and stayed there until his retirement in 1970. He became Architectural Editor and wrote descriptions of the buildings for the volumes on Soho (1966), Westminster (the four volumes on the Parish of St James's, Piccadilly, 1960) and Covent Garden (1970). During his time there the publications added 16 inches of shelf-width to the four feet amassed by this colossal research project - still in motion since it was begun by London County Council in 1900.
On retirement, the Isons sold the house in Islington to Cyril Rae and moved to Rainham Hall, Essex. This is an outstanding early-18th century brick mansion, and stepping out each morning from underneath its fine Corinthian porch put a spring in Ison's step. The last years were spent in a flat in St Leonards, East Sussex, where he became President of the local conservation society, and his last article was published in the Journal of Decorative Arts in 1982, describing the Regent Cinema, Brighton. Built in 1921 and demolished in the 1960s its gaudy style was still unfashionable when Ison wrote, and his appreciation of the quality of its decoration is all the more remarkable because he wrote from his recollections of visiting as a teenager.
Ison had a very acute aesthetic sense. His interests also included a fine collection of Chinese porcelain and of rare musical recordings; next to architecture, music was his motivating passion. The flat in St Leonards was decorated in what might be described as a pre-Colefax & Fowler Regency style. Ison, a large man, could seem formidable at first but he had a gentle and mischievous wit which remained sharp to the very end. When he and another architectural historian, Dr Mowl, disagreed on a point of Palladio's architecture he asked: "Who is this man Mole [which is how Mowl is pronounced]? He's so prickly he should be called 'Hedgehog'."
His outstanding characteristic was his devotion to Leonora and his fear that he would die first and thus abandon her. She died in November 1996, a few days after their 65th wedding anniversary. Ison talked of making a final pilgrimage to Italy but he died after a short illness.
Walter William Ison, architectural historian: born Leamington, Warwickshire 20 September 1908; married 1931 Leonora Payne (died 1996); died St Leonards, East Sussex 2 May 1997.