The Japanese delicacy fugu, or blowfish, is so poisonous that the smallest mistake in its preparation could be fatal. But Tokyo's city government is planning to ease restrictions that allow only highly trained and licensed chefs to serve the dish.

Kunio Miura always uses his special knives to prepare fugu - wooden-handled with blades tempered by a swordsmith to a keen edge. Before he starts work in his kitchen they are brought to him by an assistant, carefully stored in a special box.

Miura-san, as he is respectfully known, has been cutting up blowfish for 60 years but still approaches the task with caution. A single mistake could mean death for a customer.

Fugu is an expensive delicacy in Japan and the restaurants that serve it are among the finest in the country. In Miura-san's establishment a meal starts at $120 (£76) a head, but people are willing to pay for the assurance of the fugu chef licence mounted on his wall, yellowed now with age. He is one of a select guild authorised by Tokyo's city government to serve the dish.

When he begins work the process is swift, and mercifully out of sight of the surviving fugu swimming in their tank by the restaurant door.

Media playback is unsupported on your device Media caption Roland Buerk watches chef Kunio Miura prepare the fugu

First he lays the despatched fish, rather square of body with stubby fins, on its stomach and cuts open the head to removes its brain and eyes.

They are carefully placed in a metal tray marked "non-edible". Then he removes the skin, greenish and mottled on the top and sides, white underneath, and starts cutting at the guts.

"This is the most poisonous part," he says pulling out the ovaries. But the liver and intestines are potentially lethal too. "People say it is 200 times more deadly than cyanide."

Tetrodotoxin poisoning Numbness around the mouth followed by paralysis and death by respiratory failure - the victim remaining conscious throughout

First recorded case found in the logs of Captain Cook in 1774, after crew members ate the fish

Tetrodotoxin is named after the Tetraodontiformes order of fish, which includes blowfish

It is also found in blue-ringed octopuses, some toads, newts and other animals

Twenty-three people have died in Japan after eating fugu since 2000, according to government figures. Most of the victims are anglers who rashly try to prepare their catch at home. A spokesman for the Health and Welfare Ministry struggles to think of a single fatality in a restaurant, though last year a woman was hospitalised after eating a trace of fugu liver in one of Tokyo's top restaurants - not Miura-san's.

Tetrodotoxin poisoning has been described as "rapid and violent", first a numbness around the mouth, then paralysis, finally death. The unfortunate diner remains conscious to the end. There is no antidote.

"This would be enough to kill you," Miura-san says, slicing off a tiny sliver of fugu ovary and holding it up. Then he carefully checks the poisonous organs on the tray, making sure he has accounted for every one, and tips them into a metal drum locked with a padlock. They will be taken to Tokyo's main fish-market and burned, along with the offcuts from other fugu restaurants.

Miura-san's skill is therefore highly prized. Fugu chefs consider themselves the elite of Japan's highly competitive culinary world. He started as an apprentice in a kitchen at the age of 15. Training lasts at least two years but he was not allowed to take the practical test to get a licence until he was 20, the age people become a legal adult in Japan. A third of examinees fail.

Deadly delicacies You don't need to dine out to sup on potentially fatal fare. Did you know that these humble foods could also have deleterious effects on your health? Mushrooms, while benign in many varieties, can cause serious illness including kidney failure and even death. Rhubarb leaves are discarded in cooking as they contain oxalic acid, which can cause serious illness and in big enough quantities, death. Peanuts can be dangerous to those with severe nut allergies . Potatoes with a greenish tinge could contain glycoalkaloids which can be dangerous when consumed in large enough quantities.

So proposals by Tokyo's city government to relax the rules have been met with an outcry from qualified chefs. Coming into effect in October, they would allow restaurants to serve portions of fugu that they have bought ready-prepared off-site.

"We worked hard to get the licence and had to pass the most difficult exam in Tokyo," says Miura-san. "Under the new rules people will be able to sell fugu after just going to a class and listening for a day. We spent lots of time and money. To get this skill you have to practise by cutting more than a hundred fish and that costs hundreds of thousands of yen."

The authorities in Tokyo impose stricter regulations than any other Japanese city. In some, restaurants have already been able to sell pre-prepared fugu for a long time. And even in Tokyo these days, it is available over the internet and in some supermarkets - one reason why officials think the rules need updating.

In terms of cost, it is likely fugu would become available in cheaper restaurants and pubs (izakayas). But going to a proper fugu restaurant to eat good wild-caught fish, prepared on-site, is quite a luxury - because of the cost, if nothing else - and also quite an event. For many, playing the equivalent of Russian roulette at the dinner table is the attraction of the dish.

Some report a strange tingling of the lips from traces of the poison, although Miura-san thinks that is unlikely. He also scoffs at the myth that a chef would be honour-bound to commit ritual suicide with his fish knife if he killed a customer. Loss of his licence, a fine, litigation or perhaps prison would be the penalty.

Image caption The translucent fugu is carefully arranged in the form of petals

Miura-san serves fugu stew, and grilled fugu with teriyaki sauce, but today it is fugu-sashimi on the menu. He carefully slices the fish so thinly that when it is arranged like the petals of a chrysanthemum flower on a large dish the pattern beneath shows through.

Raw fugu is rather chewy and tastes mostly of the accompanying soy sauce dip. It is briefly poached in a broth set on a table-top burner - a dish known as shabu-shabu in Japan. The old journalistic cliche when eating unusual foods really does hold true - it tastes rather like chicken.

Fugu lovers, though, would say it has a distinctive taste, and, even more importantly, texture. Japanese has many words to describe texture because it is a very important aspect of the cuisine.

Another part of the fish's appeal is that it is a seasonal dish, eaten in winter, and Japanese diners attach a particular value to this. In the same way unagi, eel, is an important summer dish. But whatever you think of eel, it's not quite fugu - it lacks that extra thrill that comes with the knowledge that by eating it you are dicing with death.