Would madam like more fish intestines?

It was a Saturday afternoon in July when I stumbled upon my dining Holy Grail. House hunting in west London, I randomly dropped in to a small Thai restaurant decorated in garish pink, with a television beaming footage of a chef enthusiastically gutting a fish. The smell of stale seashells wafted through the room, the hustle and bustle all taking place under gilded portraits of King Bhumibol Adulyadej and Queen Sirikit.

After choosing from 101 Thai Kitchen's encyclopedic menu, the dishes began to arrive. It wasn't long before the chilli-induced tears were pooling in my eyes. Lumps of crab shell caught in my throat. Gulps of Singha beer were hastily knocked back to counter the overpowering flavour of fermented fish. It was what I had spent years searching for in London.

But could it be, I whispered to my dining companion, a little bit too authentic?

Between 2006 and 2009, I lived in Bangkok, happily paying less than a pound to bolt down a delicious dinner while teetering on a plastic stool at a street stall. Given the volume of Brits holidaying in the Far East, the increasing numbers of Thais living in the UK and the boom in ethnic-food shops, I didn't foresee any problems recreating the Thai feasts on my return. But three years had passed and despite scouring London with a group of fellow former expats, I was struggling to find the real thing. The flavours were always too muted, the sauces too gloopy and sweet, the vegetables found floating in the curries here utterly alien to menus in Thailand. So it got me thinking: do the restaurants actually know better? Is the great quest for authenticity in ethnic food a myth? When we go to our local curry house or Chinese takeaway, do we really want what is served in the train carriages of Mumbai and the factory canteens of Guangzhou? Or is it just a handful of diehard foodies and restaurant critics who want to spend their evening chewing on pig's trotters, fermented tripe and Chiang Mai sausage with blow-your-head-off papaya salad?

"When I opened, a lot of people said, 'You are mad' – not many people wanted to take that risk of using authentic ingredients from Thailand, and not substituting anything," says 101 Thai Kitchen's proprietor, Suttichai Se-Upara.

He cites the cost of importing Thai ingredients as one barrier, but concedes that many of his compatriots simply didn't think their Western customers could handle the spicy ox tripe soup, raw blue swimming crab salad and stir-fried lemongrass frog's legs that feature on Suttichai's menu. So pad thai, special fried rice and curries laden with coconut milk, sugar and Western vegetables became the norm.

Dr Kaori O'Connor, a food anthropologist at University College London and the author of The English Breakfast, says most of what we now consider to be quintessentially British food was brought from afar. The Romans, faced with a forested island with little indigenous produce, populated the land with pheasants, walnuts, apples, thyme and sage. They also introduced sausage making. "What kept on here was this tradition of English plain cooking, the porridge, the very solid bread, the cheese: plain cooking as it used to be, which is a great English source of pride," Dr O'Connor says.

This culinary exchange works both ways and has continued over the centuries as people have travelled, traded, fought, conquered and holidayed. The Vietnamese took the baguettes from their French colonial rulers and stuffed them with sliced pork, coriander, chillies and pickled carrots, creating the banh mi, a delicious culinary mash-up which you can now buy in the sandwich chain Eat.

You can still find a variation on the schnitzel on some menus in Samoa – "in utter defiance of the climate" – a legacy of a very brief German occupation before the First World War, says Dr O'Connor. Kedgeree was the ultimate twisting of Indian food for the tastes of the British Raj, but no one complains that it's not authentic: it is celebrated as a dish in its own right.

In Britain, the explosion of package holidays in the 1960s also contributed to a change in people's tastes. "They run into spaghetti for the first time and it's all glam," Dr O'Connor says. "You get first the wave of continental food reintroduced after the wars, then people go further afield and then more and more foreign people move here and it just gathers steam."

Now it is as much about marketing and trying to work out what will sell. As the big Western chains branch out across the globe, they tap into the local tastes. You can get a Big Spicy Paneer Wrap at McDonald's in India and a McSatay in Indonesia. Wendy's in Japan offers a lobster burger: its marketing told it the Japanese wanted seafood in a bun.

"Food is a business. If they don't appeal to the palate and you have to start slowly, then you're going out of business," Dr O'Connor says. And that is exactly what most Thai-restaurant proprietors are doing here – adapting their cuisines for what they hope will be greater profit. But while this made sense when migrant communities were first taking back unimaginably exotic ingredients to a post-war country that had only just got to grips with bananas, surely now things have moved on?

To put this theory to the test, I gathered my group of friends at 101 Thai Kitchen and asked them to order the dishes they missed the most, as well as a few surprises. The verdict was unanimous: it was utterly delicious and the most authentic Thai food any of them had eaten in the UK. But faced with Suttichai's southern speciality gaeng tai pla – fermented fish intestines swimming in a pungent brown broth – even Thai-food-hardened former expats struggled.

"However much I want to taste it for your article, I just don't want to taste it," protested my friend Claire, who worked for a charity in Bangkok for three years. Everyone eventually sampled the curry, with reactions ranging from the polite – "It's a bit salty" – to the more extreme.

"It's like snorting a fish, including the bones," was the verdict from Paul, a lawyer whose work had taken him to the very province the dish hailed from. The rest of the fish-gut curry remained untouched, proof that even those of us who lived, worked and dined in the region struggle with some of the more feisty regional delicacies.

And while Suttichai insists Westerners are nowadays more open to new flavours, among the 15-odd pages of exotic dishes on offer, pad thai remains 101 Thai Kitchen's most popular choice among non-Thai clientele.

Dr O'Connor says that in a few generations, eating a curry has gone from being suspect to standard. But she thinks there is a fair way to go before we're all snacking on boiled chicken's feet at our local Guangdongese: "Now it's out there and you can navigate your way to it, but for most people, they like the mainstream."