Among the tartan tea towels and toy Highland terriers, one of the most popular souvenirs at the Museum of Scotland in Edinburgh is a set of coffee mugs celebrating the invective genius of the Scots tongue. Each one bears the definition of a word. A numpty is an idiot. Glaikit folk are senseless. Someone who blethers talks to no purpose. Has a language ever been so well equipped to abuse? Yet even in this argumentative nation, vernacular sometimes fails. New superlatives of vitriol have to be found, even if that means resorting to English.

In the eyes of his enemies, Michael Fry is more than just a blethering glaikit numpty. Fellow historian John Macleod calls him a “large complacent Edinburgh lounge lizard”, adding “I will repeat those words very slowly to make sure you write them down.” The West Highland Free Press dismisses him as “a boorish inebriate with an eye to the main chance”, while in the Scottish parliament a motion has been lodged deploring his views. To Brian Wilson, a former Labour minister, Fry is not only “a buffoon” but comparable to the Holocaust-denying historian David Irving.

What has Fry done to attract such attention? The answer may surprise many who are not Scottish. The historian’s offence has been to question events that took place more than a century ago. In his book Wild Scots: Four Hundred Years of Highland History, which is published by John Murray on Monday, he assaults what he sees as the mythology of the Highland Clearances.

The Clearances, which took place between the late 18th and mid-19th century, tend to be considered the greatest tragedy of Scottish history, a series of coercive and often violent evictions that tore the heart from the Highlands, and from which the region has still not recovered. When this story is told, words such as “genocide” and “ethnic cleansing” are rarely far away.

In the popular imagination - inspired by John Prebble’s 1963 bestseller The Highland Clearances - it has become a tale of evil landlords who, finding their estates unprofitable, evicted tenants from long-held plots of land in order to graze sheep. The estate owners (euphemistically perhaps) called this “improvement”.

The most famous and reviled “clearer” was Patrick Sellar, the “factor” or land-manager for Lord Stafford - later the first Duke of Sutherland. Stafford was one of Britain’s richest men at the start of the 19th century. His estate north of the border - which had been inherited by his wife, the countess - covered a 20th of Scotland. Yet the couple visited it rarely. Such absenteeism put huge power in the hands of Sellar, who abused it terribly. In June 1814, he carried out evictions in the valley of Strathnaver, which runs from moorland into the Atlantic on Scotland’s north coast. As families were forced from their houses, the timbers were set alight to stop them returning.

According to one account, when Sellar came to the house of one William Chisholm, he found Chisholm’s bed-ridden mother-in-law. Told that she was too ill to be moved, the factor is said to have replied: “Damn her, the old witch; she has lived too long. Let her burn!” Her blankets were alight as one of her family carried her to a nearby shed. Five days later, she died. One Gaelic poet wrote of Sellar: “If I had you on the field and men binding you, with my fists I would tear out three inches of your lungs.”

But it was not just the manner of some evictions that cemented the Clearances’ place in the Scottish psyche. Many of those “cleared” ended up farming unproductive strips of land by the coast. Since this was not enough to live on, often they harvested kelp. This soul-destroying work involved standing up to the waist in freezing water for long periods. The seaweed was used to make soap and glass. Wages - set by the same landlords who ordered the evictions - were low, even before the kelp market collapsed disastrously at the end of the Napoleonic wars in 1815.

Many Highlanders moved to the slums of Edinburgh and Glasgow. Thousands more went abroad, mainly to Canada, the number increasing as the prospect of starvation gripped the Highlands after the potato famine of the 1840s. The privations of such voyages - decks awash with excrement, outbreaks of typhoid and cholera - have often been commented on. Dozens of rotten-timbered boats failed to make it across the ocean.

It is a grim tale, and Scotland’s politicians have never been slow to find echoes in absentee landlords plundering a disenfranchised people. As Neil Ascherson writes in his book Stone Voices: The Search for Scotland: “Few nationalisms do not incorporate a wound.” For many, the Clearances still purposefully fester.

”They have certainly been very useful to the left,” says the novelist and political commentator Alan Massie, a lowland Scot and a Tory. A great grievance for nationalists in the 1970s was the British government’s appropriation of revenues for “Scottish” oil, discovered in the North Sea. The playwright John McGrath made the connection with the Clearances explicit in one of that period’s best-known Scottish plays, The Cheviot, the Stag and the Black, Black Oil. (Cheviots are a breed of sheep introduced to cleared land.)

In the 1980s, as Scotland’s heavy industries suffered under a Conservative government with little support north of the border, the symbolism was simpler. “Crudely, you might say, ‘Thatcher equals Patrick Sellar’,” says Massie.

The Clearances have also offered a historical crutch to both Labour and Scottish National Party politicians pursuing land reform in Scotland. Rob Gibson, the SNP member of the Scottish parliament who introduced the motion condemning Fry, is among them. “The concentration of land in Scotland rests with a very small handful of landowners still,” Gibson argues. The Clearances have left “unfinished business”.

Another great Scottish word is stooshie, meaning fight. By contesting the received wisdom of the Clearances, Fry has created an almighty stooshie. “Clearances - what clearances?” read the headline on one article he wrote for the Scottish Review of Books. The standard view of what happened, he says, “exposes a defect in the current state of Scottish psychology. It is evidence of mental illness that Scotland is interested only in those aspects of her history depicting Scots as victims.”

It is lunchtime on a fine June day in Edinburgh, and Fry is in the Tower restaurant, four floors above the National Museum gift shop and its intemperate mugs. Evidence of Scotland’s complex relationship with its past is all around. Through the window, Edinburgh Castle fills the skyline. Across the road, the British flag and the Saltire flutter side by side, symbols of a country whose history has been defined by the tension of nationalist dreams and unionist reality.

But you needn’t go far to find another brand of Scottish history. A two-minute walk brings you to the Royal Mile, with its ghost tours and kilt shops. The blend of myth and reality peddled here is so well-mixed that most Scots - let alone tourists - have no idea where the facts end and the love of a yarn begins. The same is true of Rob Roy and Mary Queen of Scots, the battle of Bannockburn and William “Braveheart” Wallace.

Against this national tendency to play fast and loose with historical truth, Fry’s revisionist take on the Clearances makes its stand: “The things I have to say cannot just be answered by abusing the person who reports them. There’s a lot wrong with modern Scotland that’s connected with wrong views of Scottish history,” he says. “My work is about helping the country to understand its identity, which it is still quite a long way from doing.”

And if he offends a few people and takes some stick along the way, so be it. Fry is used to the latter and seems to enjoy the former. Having once stood as a Tory candidate in staunchly Labour Glasgow Maryhill, he is not unaware that his Thatcherite views stick in the craw of many fellow Scots.

Potential constituents were unlikely to have been won over by his delight in playing the bon viveur, a gentleman scholar who writes in the morning and lunches in the afternoon. At our lunch, he consumes a gin and tonic, oysters washed down with a bottle of claret, a steak as thick as a telephone directory and a plate of cheese. This is followed by several pints at a nearby pub, after which he departs - scarcely the worse for wear - for another dining engagement. He is huge and suffers from gout. After interviewing him, I briefly considered having a T-shirt made up with the words “I have been lunched by Michael Fry - and lived.”

None of this excess, however, has sapped Fry’s productivity. His study of the 18th-century home secretary Henry Dundas was widely praised. Neal Ascherson - hardly a political bedfellow - describes Fry’s huge account of Scotland’s role in the British Empire, The Scottish Empire, as “a truculent masterpiece”. Rob Gibson’s parliamentary motion of censure, lodged in March, petulantly places quotation marks around the word “historian”, as if questioning Fry’s right to the title. On that account, at least, it is wrong.

In Wild Scots, Fry’s attack on the “myth” of the Clearances is more nuanced than some of his pre-publicity might suggest - inevitably, since it is dealing with a process that took place across a large geographical area and over more than a century.

Broadly, though, it rests on three assertions. First, that the Highland population rose, not fell, over the period in question. Second, that where emigration happened it was often voluntary; people chose to better themselves in the New World. And third - most contentiously - that, in forcing tenants to move, many landowners acted benevolently.

”Although the book has been stigmatised as ‘Clearance-denial’, I do concede Clearances took place, some perhaps coercive,” he says. “But that is not the whole story.” A booming population meant that the small plots traditionally farmed by the peasant tenants were being sub-divided until they barely provided subsistence.

”What happened is that people were shifted from this unproductive, half-starved way of life in the glens, so they could earn a better living. I don’t see this as a great tragedy. Nor is it genocide by any stretch of the imagination.”

For the estate owners, Fry argues, self-interest and philanthropy coincided. “Where they made profits from renting their land for grazing or whatever, it was passed down in public works, such as road-building. Schools, churches, all these things were built by landlords. So they did reinvest profits in the land.” Many landlords, reluctant to see their people emigrate, went bankrupt trying to support them. Rising population and failing crops made their efforts futile. In the end, many Highlanders had to emigrate. But they did so in spite of, not because of, decades of “improvement”.

In Scotland today, the first Duke of Sutherland is so reviled that there have been persistent campaigns to demolish his memorial, an imposing 30ft-high sandstone statue set on a column near Golspie. Yet Fry points out that the £250,000 he spent on his lands represent £100m at today’s prices, “a straight transfer from England and a hefty dose of regional aid by any standards”. The duke, he argues, was a well-intentioned if misguided social engineer, and Patrick Sellar simply an over-zealous subaltern. The “forlorn settlements for the dispossessed on the coast of Sutherland” were precursors of the blighted post-war high rises to which Edinburgh and Glasgow’s urban poor were moved by the Labour government - also for their own good.

Fry’s idea that the Clearances were driven by the forebears of the modern left is an irony to savour as one would the finest Loch Etive oyster.

But all this metropolitan prattling about the Highland experience does not go down well on Lewis in the Western Isles, the site of various clearances. “What do I feel when you mention the Clearances?” says the writer John Macleod, generations of whose family have lived there. “White-hot anger.”

Macleod has not read Fry’s book; but he has seen his journalism on the subject. “In his own field, he is a very good historian,” he says. “But he has to realise he is causing great and genuine hurt.”

For many in Scotland’s Highlands and Islands, he adds, the Clearances seem relatively recent, their memory passed down the generations. In the 1840s, Macleod’s own great-great-grandfather, Angus Macaulay, was evicted from Knip to Shawbost, almost 30 miles away. “He might as well have been sent to Yugoslavia.” Another great-great-grandparent, Catherine Maclean, was moved to “a swamp” on Sir James Matheson’s Lewis estate. Catherine was outside one day when Lady Matheson stopped her carriage and bid the girl approach.

”It was terrifying,” Macleod says. “In those days, the worst you could do was draw attention to yourself.” The girl grovelled and a flattered Lady Matheson promised to send her a piece of cloth. What colour would she like? “Whatever colour you desire, ma’am,” she replied.

Matheson had a reputation as an enlightened landlord, but his factor Donald Munro was feared. Munro’s posts included justice of the peace, public prosecutor, military commissioner and electoral officer. “All power lay in his hands,” Macleod says. On the island, though, he is best remembered for a threat: “I’ll have the land off you.” When he was an old and broken man, children taunted him with the same words.

Hundreds of functionaries such as Munro ruled the Highlands: it was an era of fear. Yet the uniqueness of the tragedy, according to Macleod, was the devastation it wrought on Gaelic culture and language: “Villages were vaporised.” In his 1997 book Highlanders he writes: “To call the Clearances ‘the Highland Holocaust’ is to insult the real Holocaust and the 14 million Europeans who died in it.

”Yet it was perhaps a holocaust of sorts. A burned offering, not only in smoke and thatch and sticks, but the destruction - utter and irreversible - of ancient, irreplaceable things.”

Fry’s response is less lyrical: “Economic circumstances change. I certainly have no attachment to a certain way of life being hallowed by history and entitled to claim immunity.”

Such bluntness, bordering on insensitivity, has fuelled the row. “You can say why the Clearances were unavoidable,” adds James Hunter, a former chairman of the development agency Highlands and Islands Enterprise, and a respected historian. “But it’s a historian’s duty to take full account of the human cost. In that area, Michael has lacked.”

Yet Hunter concedes Fry’s right to start a debate. By contrast, there is a hectoring authoritarianism to Rob Gibson’s criticisms that sits uneasily with a member of parliament. “The kind of ultra-conservative, almost neo-con, language Fry uses is quite unacceptable in Scotland,” Gibson says. “I think he is going against the grain of what people in Scotland want now,” he adds, as if a historian’s job (or duty) was simply to reinforce a nation’s image of itself.

Gibson won’t lack supporters. But I suspect there will be more Scots who think their parliament, established in 1998 after a long struggle, should have better ways to spend its time than rubber-stamping an official version of history.

The outspoken Scottish composer James MacMillan puts this succinctly. In May he entered the fray by dedicating a new choral work commissioned by Yale University, Nemo te condemnavit, to Fry. The reaction to Fry’s work, he railed, “puts us up there with the Nazi Reichstag and the Supreme Soviet Assembly as a parliament with an instinct for banning writers. What’s next, a mass burning of books which do not receive the imprimatur of the Scotia Nostra?” Even in a country that excels at insults, that represents a palpable hit.