Almost single-handedly, Augustus Welby Northmore Pugin propelled Britain into the Gothic Revival, a style familiar from innumerable Victorian parish churches and town halls; but, in doing so, he cast a blight over British architecture which lasted long after the Gothic Revival began to falter in the 1860s, a blight from which it has never recovered. Above all, he introduced the fatal notion of stylistic intolerance into British architecture - the belief that there is only one way to build, one style to follow, and that to build in any other way is not only wrong but immoral.
This is not to deny that A W N Pugin was touched by genius. At 15, he was designing furniture for Sir Jeffry Wyatville's rebuilding of Windsor Castle in 1827. His hand is everywhere at the Palace of Westminster, from the design of heraldic animals to thrones, fire-irons to crockery. By the time he died, burnt out and more than a little mad, he had six cathedrals, more than 40 churches and numerous seminaries, convents, monasteries and houses to his name. He was only 40, but his influence on architects in Britain, and indeed across the world, was already profound.
Pugin was a great propagandist. He had to be to achieve such rapid personal success and subsequent influence. And, like most great propagandists, he relied on the simplistic image. The famous illustrations in his book Contrasts showed the same scene in the Middle Ages and the 19th century, the one a lost medieval world free from ugliness and dirt, the other a world of villainous, ugly modernity. There can be no doubt which the viewer is supposed to prefer. His drawings are the lineal forebears of innumerable architects' impressions in the middle of the 20th century advocating wholesale redevelopment in which the sun only shines on the buildings they have designed. So powerful was the effect of this propaganda that, nearly a century and a half after his death, architectural commentators still look at Gothic architecture through the prism of Pugin's prejudices. One of the curators of the Pugin exhibition casually dismisses 'the sham of 18th-century Gothic'. He does so because, to him, only Puginian Gothic, with its accurate reconstruction and its obsession for form following function, is true Gothic. The Georgian Goths, whose interest lay in antiquarianism and historical association, are still put down today with the diminutive 'Gothick', to ensure no one confuses their work with the real thing.
It was not just the reputation of Georgian Gothic that suffered from Pugin's success. The high art of British Classicism was effectively killed off, too. The architectural historian Sir John Summerson, with the Modernists' presumption that styles cannot coexist but must succeed one other, assumed that 'the last great chapter in the history of classicism was closed' by 1830. But no style that was still capable of producing architects as innovative as G R Cockerell and, in Scotland, Alexander Thompson could be described as finished. Until Pugin cut the ground from under its feet with Contrasts in 1836, Classical architecture happily coexisted with Gothic buildings, to the greater richness of Britain's architectural tradition. Pugin ended this tolerant pluralism, forcing a crisis of confidence from which the Classical tradition in this country has never quite recovered.
With it went the pragmatic approach that had been so characteristic of Georgian architecture. Classical architects in the 17th and 18th centuries had seldom been ruled by dogma; their work was based ultimately on convenance, or propriety. Instead of deciding on a style - or rather identifying the appropriate manner that they felt formed 'the spirit of the age' - and forcing clients and buildings into that straitjacket, they found the style appropriate to the commission. Classicism was preferred, but if a client wanted to assert the antiquity of his house or to evoke the exoticism of the Orient in his garden, then they were perfectly happy to design in Gothic or Chinoiserie.
Pugin's intolerant belief that there was only one way to build, regardless of practicality, was his most damaging legacy. Generation after generation of architects, particularly recent architects, have based their design philosophy on a tradition that goes directly back to Pugin: there is only one manner or style in which to build at any one time - and the architect knows what that is. The damaging division between architects and the public stems largely from that belief. So does the inability of many architects to accept that, given the complexity of late 20th-century society, different styles are appropriate for different sorts of building.
Perhaps that is why Pugin is being rehabilitated today. He provides the perfect precedent for Modernist architects convinced that there is only one way to build - theirs.
The author is architectural editor of 'Country Life'.