When I first heard a chippie in Edinburgh was serving deep fried Mars bars, I assumed it was a joke. It was not until, queuing for a fish supper one night in the Royal Mile and seeing them on the blackboard I realised that what had sounded like a gastronomic irony was in fact a heart-stopping reality, an edible paradox in the same vein as Baked Alaska.

But where ice-cream cocooned in hot meringue is an exercise in contrasts and culinary skill, the frying of chocolate-coated confectionery comes into the category of bad taste, on every level. How is it, then, that this most revolting and calorific dish is now almost as well known an item on the Scottish menu as shortbread and whisky?

According to Dr Christine Knight, from the University of Edinburgh, the reason is simple. As she will tell a conference this weekend at Queen Margaret University, the deep fried Mars bar is nothing less than a political weapon, an agent of oppression as well as provocation. The danger it poses to the individual’s health is as nothing to that it has upon the body politic. This gnarled golden ingot, more like a relic picked off a shipwreck at the bottom of the sea than anything you’d want to sink your teeth into is, she tells us, a “shorthand for poor Scottish nutrition, health and obesity rates, simultaneously communicating derogatory messages about taste, class, morality and the Scottish nation itself”.

Where once the humble haggis – a sheep’s bladder stuffed with peppery offal – was the mainstay of cartoons and satires about a people deemed primitive and uncouth, now confectionery sizzling in the fryer has taken on the role. Nor is it only our naysayers who promote the idea of a nation trailing the scent of cooking fat behind us as proudly as if it were Chanel No. 5. We are only too keen to add to the myth ourselves. One fast food emporium I passed recently boasted that it could rustle up fried Mars bars, but would also “fry anything”.

All of this would be funny, if it weren’t so serious. Every country has its culinary peculiarities, those recipes it takes time to learn to love. In Italy it’s tripe, whose appearance on one hapless diner’s table next to mine turned his face the colour of curdled milk, and was sent straight back to the kitchen.

Londoners’ fondness for jellied eels and jars of whelks turns my stomach, but my Cockney grandfather never lost his taste for them. Yet when people speak of Italian or English cuisine, it is pecorino and olive oil or warm beer and roast beef that are first mentioned, not items that only connoisseurs of the slithery enjoy.

Not so in Scotland, where since the middle ages our food has, unfairly, been a source of mockery and derision. Dr Knight contends such stereotyping can be linked to times of unease with our southern neighbours, such as the independence referendum or, in the 18th century, the union of parliaments and the Jacobite risings.

While such insults perhaps increased during these periods, to judge by accounts from travellers of other centuries, food was almost always an issue, regardless of political tensions. Some of that was to do with scarcity, or cleanliness, but it’s fair to say the plainness of our ingredients came as a shock to some.

When you now consider how greedy and over-fed many of the well-off were, however, those visitors who turned up their noses at herring, porridge and kale might have lived longer had they embraced our leaner, healthier, vitamin-packed fare.

Sometimes, of course, it was so meagre it prefigured the 5:2 diet. As a character piquantly says in John Galt’s novel The Entail: “Ye had better come hame, for there’s a sheep’s head in the pat, wi’ a cuff o’ the neck like ony Glasgow bailie’s. Ye’ll no get the like o’t at Kilmarkeckle, where the kail’s sae thin that every pile o’ barley runs roun’ the dish, bobbing and bidding gude-day to its neighbour.”

Peasant food was common across Europe, but extracting political capital from it seems a Scottish speciality. With the advent of the deep fried Mars bar, the jibes it raises are arguably even more offensive than those at the haggis’s expense. Where once it was our perceived backwardness or barbarism that was being pilloried, now it is our eagerness to eat badly, reinforcing the country’s image as the sickest in the EU.

While one can dine upon some of the finest foods in the world from a Scottish plate, the deep fried Mars bar alludes to our supposedly incurable preference for orange food, the sort that wouldn’t allow a vegetable or a vitamin to touch it, and which looks as if it has just survived a nuclear attack.

As in food, so in other realms of life. Perceptions, once engrained, are fiendishly difficult to alter. When No Mean City was coined to describe Glasgow, hinting at its thuggish credentials, its PR fate was sealed for a century at least.

The same goes for the nation’s supposed tight-fistedness, even though statistics invariably show our donations to charity outweigh the rest of the UK. Many of these stereotypes are perpetuated by outsiders, but we are a little too willing to pillory ourselves as well.

Where other countries are adept at self-promotion, ceaselessly talking up their food and culture as if they were paid by the boast, we sell ourselves short at every turn. It is as if we are secretly impressed by our history of pugnacity, quixotic weather, and aversion not only to haute cuisine but anything remotely resembling a balanced diet. Thus a culture that revels in excessive drinking and artery-clogging fats has evolved, reflected in novels and films dominated by hard-living, tough-hearted men whose livers won’t see them through the weekend.

Stuart Cosgrove famously ruffled feathers by denouncing our remorselessly downbeat film industry. While English films and TV series are distinguished by the feel-good, such as Notting Hill and Downton Abbey, in Scotland for far too long it was typified by Trainspotting, Shallow Grave and Morvern Callar. Gradually, of course, all this is changing to offer a more nuanced picture, be it with films like Sunshine on Leith, books such as 44 Scotland Street or our growing number of Michelin-starred restaurants, and food writers such as Claire Macdonald and Tony Singh, whose emphasis on fresh, local produce is helping to transform the cookery bookshelf.

Yet there is much more to be done, and some of it falls to us. When visitors mention the infamous Mars bar, we should counter with talk of langoustines and organic lamb. When Mediterranean guests deplore our lack of sunshine, we should mention the dictionary of words we have for rain, and its benefits for the complexion and our gardens. The means at our disposal for altering our image are countless. But perhaps as the summer marching season approaches we could do worse than start by holding anti-orange demonstrations, waving leeks and bouquets of brussels sprouts above our heads, and discarding our deep fat fryers at the nearest tip.