^"It's absolute nonsense to say that I'm a fogey!" says Simon Thurley. But that is the charge that the chief executive of English Heritage has faced recently for his new book, The Building of England, a 544-page history that starts when the Romans left in 410 and ends when the Luftwaffe arrived in 1940. It's precisely that cut-off point that leads to the charge of conservatism. "Thurley is inclined to fogeyish nostalgia," wrote Richard Morrison in the Times. "Unfortunately, he stops his survey after 1930, as though he can't bear to contemplate the glass towers that now dwarf his beloved abbeys and terraces … But most of us live and work in an England built since then."

Modernism figures for a paragraph, and then only when Thurley insists on its relative unimportance. AN Wilson called Thurley's book an instant classic that married the imaginative flair of John Betjeman with the learning of Nikolaus Pevsner, and added that he had bought five as edifying Christmas presents – an encomium that, one might think, clinches the fogey charge.

Thurley, though, refuses to accept that his book ignores what we live in. "Richard Morrison's wrong there. Most people do not live in modernist buildings. The vast majority of people in this country live in buildings built in the interwar period – that's when the housing stock increased by millions and millions."

He's happy that so few Britons live in a Le Corbusier-like utopia or post-modern fantasyland. "I just don't agree with the notion of progress. I don't think it is necessarily progress to consume a vast amount of energy just to stay static. Any tower block has to have its air conditioning on 24/7. Glass and steel use huge amounts of carbon to make them. Cutting stone out of the ground and cutting down trees don't. I'm not saying the Gherkin isn't a beautiful building because it is, and the Cheese Grater is great, and actually I think the Shard isn't a bad building either, but I just don't think they in absolute terms represent progress on a Georgian terrace house. I just don't."

The fact that Thurley doesn't believe in architectural progress gives the book its singular perspective on how buildings shaped, and were shaped by, the English. Instead of the arrow of progress, he offers a pendulum account: the English have run from ornament to austerity and back again. "We've seen that in our lifetimes. Critics have given the name post-modernism to buildings like Terry Farrell's TV-am building with the egg cups on the top in London's Camden. That was the swing from minimalist no decoration coming back to decoration and fun. It'll go back."

But not for long. The English, he maintains, have what he calls "a sweet-tooth aesthetic", a taste for ornamentation. That taste, he suggests, explains why each square metre of Lincoln Cathedral cost 10 times more than its French equivalents.

"Do a circuit round St Paul's Cathedral," he counsels. "It is full of small-scale, quite fussy decoration. I was in Paris at the weekend and walking around the parts of the Louvre built at a similar period to St Paul's, and I noticed the cleanliness of the lines, the orders of architecture managing to speak and express themselves against masses of stonework. That doesn't really exist here. Every time English architecture has tried to be austere and plain, very quickly it has acquired decoration. I think that is the story of it all."

Forget, for the moment, about cathedrals and the other venerable glories of English architecture. Thurley contends he has spent the last 12 years at English Heritage trying to save postwar British buildings that his critics charge he has sniffily airbrushed from his history. "I have been consistently a champion for listing postwar buildings, and in fact we've done more for postwar building types than for anything else. It is the big threat area."

Consider Preston Bus Station. Ove Arup's 1968 brutalist classic was, in 2000 and 2010, threatened with demolition and English Heritage's application to have it listed was repeatedly rejected. "I like Margaret Hodge but I disagreed with her over the listing of postwar buildings," when the Labour MP was minister of state for culture and tourism in Gordon Brown's administration. "She just didn't like brutalism. Lots of people who lived through the erection of those buildings don't like them." In the case of Preston Bus Station, it was left to Hodge's Conservative successor to list it – a source of great pride for Thurley.

The ostensible fogey, then, is English brutalism's greatest champion. That said, he failed to save two other brutalist favourites: Owen Luder's Tricorn Centre in Portsmouth and his Gateshead Car Park, the latter made famous in the film Get Carter. Surely an iconic scene in a Michael Caine classic is sufficient to warrant a listing? "We have very strict criteria for what gets listed and it just didn't make the grade."

But fighting for those officially unloved local buildings (the postwar redevelopment of Plymouth's war-bombed city centre, say, or the ziggurats of student accommodation at the University of East Anglia) that he and his colleagues think great has been the chief focus of Thurley's tenure. He's lost the battle over another ziggurat, Birmingham's central library, once described by Prince Charles as looking like "a place where books are incinerated, not kept" and now replaced by a gaudier confection on Broad Street. "I'm very sad we didn't manage to save it. It's a great building."

Perhaps, but I remember interviewing Birmingham's head of libraries, Brian Gambles, in 2010 when he showed me a chunk of concrete that had fallen from the library as evidence for the need to demolish it. "Repair it in that case," counters Thurley. "If a lump falls off Salisbury Cathedral you don't say knock it down."

If Thurley is a defender of English postwar architecture, why didn't he celebrate it in his book? "Some people have said to me I could have taken it up to the festival of Britain 1951. I could have ended with Coventry Cathedral and Festival Hall, which perhaps would have been more logical to end with than the BBC and Riba. When it comes out in paperback we may find that the story has sneakily slipped to 1952 if my publisher will let me."

But no later than that, because of Thurley's methodological scruples. "Because the war seems such a long time ago we don't realise that when people write histories of the architecture of our era we will be in a chapter called postwar. The history of Britain after the war will be the history of the big state – the NHS, public ownership, all that. Only now, as a result of austerity, are we are beginning to move out of the postwar chapter into another. And I think when that happens and when we've got enough perspective to see that it's happening, I'll write that chapter."

We're sitting in a restaurant in the conversion of Lewis Cubitt's 1852 granary buildings at the heart of the King's Cross goods yards in London. In his book, Thurley eulogises the granary as "a heroic composition flanked on either side by transit sheds. Six storeys high with a deep cornice and a parapet, its facade has four shallow projecting bays like giant Doric pilasters." Once it was the largest transport interchange in England where the ages of horse, canal and steam came briefly together to distribute goods and raw materials from and to the capital. Thurley loves the granary building as an example of England's industrial heritage. "We're a great nation of engineers, and some people might argue that our engineering skills are better than our design skills. I wouldn't know about that." Very diplomatic – given that the granary now houses Central Saint Martins College of Arts and Design.

But where English architecture ends and engineering begins is a moot point. "From where I'm sitting," he says, "I'm looking at the most fantastic piece of engineering, the engine sheds at King's Cross. And if I was sitting where you're sitting I might be able to see the Barlow engine shed at St Pancras. These structures were totally pushing it. Look where international hi-tech came from. It came from English – or rather British – engineers and architects."

Thurley's love of old buildings came early. He was born in 1962 and brought up by religious parents who took him to church three times on Sundays. "We lived in a former Strict Baptist manse," he recalls. In the garden of that manse, in Godmanchester, Cambridgeshire, Simon watched archaeologists excavating gardens. Aged seven, he was digging in the family vegetable patch and hit what turned out to be a rubbish pit at the back of a Roman shop. "The next summer our dig led to the discovery of a Roman basilica. Our lawn was never flat enough to play cricket on again."

Such childhood forays into archaeology led to him reading history at the University of London. He did his MA in architectural history at the Courtauld Institute and then a PhD on Tudor royal palaces that was published by Yale University Press in 1993. It was the start of a literary career writing huge, lavishly illustrated books on architecture: when Bill Bryson chose Thurley's 2002 book on Hampton Court as his book of the year he wrote: "The only downside is that if you fall asleep reading it in bed, you could be crushed."

Happily for his career if not for the built environment, soon after completing that doctorate, one of those Tudor royal palaces burned down. Following the terrible fire at Hampton Court in 1986, English Heritage recruited 26-year-old Thurley as assistant inspector of historic buildings and ancient monuments to work with the team restoring the palace. Later he became a curator of the Historic Royal Palaces, the body that now runs Hampton Court, the Tower of London and Kensington Palace, working on the restoration of William and Mary's Privy Garden at Hampton Court and rebuilding the Jewel House at the Tower of London to house the crown jewels.

He was director of the Museum of London from 1997 to 2002, during which time he married Katharine Goodison, but the couple divorced in 2007. The following year he married historian Anna Keay, who is currently director of the Landmark Trust, with whom he had worked at English Heritage and on the 2006 Channel 5 series The Buildings That Shaped Britain.

The couple live with their five-year-old twins in a Grade I listed medieval merchant's house in King's Lynn, which Pevsner described as "the most remarkable catalogue of building periods from the middle ages onwards". It's there that Thurley wrote The Building of England while his wife finished her biography of the Duke of Monmouth. Occasionally they offer guided tours of their home, along with coffee and homemade cakes.

Even if Thurley's happy combination of the professional and the personal sounds idyllic, his job naturally involves a lot of criticism, no more so than last month when English Heritage's new visitor centre at Stonehenge was branded a "£27m flop". Visitors railed against waiting more than an hour to board the land train (a Land Rover pulling three carriages) to ferry them from visitor centre to stones and back. The debacle pained Thurley. In his 2012 book Men from the Ministry: How Britain Saved Its Heritage, he had a chapter on how Stonehenge had been saved from vandals and profiteers. Was it reverting to national disgrace on Simon Thurley's watch?

^'We had six days of bedlam," he concedes. I put my hand up and say that the building was never designed for 1,000 people an hour. We were totally victims of our own success. Anyway we've sorted out the problem now. So half term? Bring it on!"

We wander around the redeveloped King's Cross goods yard. What's his most significant achievement at English Heritage? Saving a brutalist bus station or a derided hall of residence? Neither. "I'm most proud of changing the way people think about heritage. Heritage is about the future, really. It's not about the past. People think people in heritage want to stop things happening. What we actually want is to make sure that the very best parts of our nation's past become parts of our future.

"I wanted to meet you here because here you have this fantastic part of our past completely redundant from its original purpose." When it was a goods yard it would have been a hidden gem. "That's right. No one would have come here who didn't work here. It would have stunned the original constructors to think centuries later we would be appreciating their work or that students would make these old buildings as lively as they once were but in an unimagined way. What a wonderful thing for the future of England! That for me is what heritage means."