The story of sushi goes back to prehistoric Southeast Asia.

There, fish was preserved by packing it with salt and cooked rice, resulting in a vinegary, fermented fish and a gloopy rice⏤the rice part was truly disgusting and usually discarded.

In Japan, where the technique remained in use as it died out elsewhere, it was called "nare-sushi", "nare" meaning "aged".

This was the definition of sushi for several centuries.

But by the 15th century, especially in coastal areas where fish was more plentiful all year round, people were leaving it for less time and daring to eat the rice, which, eaten early, was pleasantly tangy.

Two hundred years later, with Japanese demand for the taste of sushi booming, an even quicker version was invented, which involved simply adding vinegar to the rice to flavor it.

Finally, in the 1820s in what is now Tokyo, raw fish⏤as fresh as possible⏤was added to the rice, now no longer aged at all, and modern sushi was born.

The Japanese called it "haya-sushi", "haya" meaning "fast".

Japan was a very closed country until 1854, so it wasn't until the late Victorian period that Westerners, particularly Americans, started spending time in Japan and encountered sushi.

It required an incredible level of skill; getting it wrong wasn't just annoying, but potentially risky.

One rare delicacy, pufferfish, which today is tightly regulated, is highly poisonous if badly prepared.

It wasn't until the 1970s that sushi, both as a luxury treat and as a cheap street food, started to be seen outside Japan.

It first emerged in California, which had a large Japanese population, and followed the Japanese across the world.

Californians, initially aghast at the idea of eating raw fish, grew to love it.

But, to encourage them, Japanese sushi chefs came up with the Californian roll, which originally contained cooked crab.

Other Westernized recipes followed, including the decidedly 1980s Philadelphia roll, with smoked salmon and cream cheese.

Most Western countries don't allow fresh raw fish to be used because of the danger from parasites; fish must be frozen, which kills the parasites, before use.

As sushi spread, the deeply ingrained Western fear of raw fish meant that more and more versions came into use which relied on ingredients such as cooked prawns, smoked fish, or egg.

And where the often complex side sauces were replaced with simple soy sauce, ginger, and wasabi.

The ultimate Westernization is probably the Asian-Latin fusion, which is the sushi burrito invented in 2011.

The first sushi restaurant in the UK opened in London in 1994 in the city, the heart of business land.

Today, sushi is booming, marketed as being healthy, convenient, and, still, just a little bit exotic.

The conveyor belt concept used in many restaurants adds a certain level of novelty, as do the chopsticks, although, according to many Japanese, sushi is best eaten with the fingers.

Today, there are many types of sushi.

At its best, it is often still very expensive and very beautiful, and its devotees can be positively fanatical.

A Japanese apprenticeship lasts at least five years for a sushi chef, and both Japan and the UK have sushi restaurants which have been awarded three Michelin stars.

Not bad for a food which started as a way to stop fish from rotting.