It’s a hot day, you fancy an ice cream and the familiar curvaceous van has just warbled round the corner. But excuse me, I must sound terribly old-fashioned.

When I say ice cream, I really mean a “wrapped impulse product”, preferably one that represents “the essence of the pursuit of self-indulgence”. As for the van, well, forget simple ditties, Italian names and “mind that child” signs. We’re talking disc-jockey sound systems to entice customers. We’re talking choice of “wrapped impulse”, courtesy of interactive plasma screens. And we’re talking must-have accessories. Just buying a Magnum is to become a “fun experience” intended to let you “break away from hectic modern life”, according to the man responsible.

That man is Robert Polet, global ice-cream president of Unilever. This summer, the multinational is making its biggest-ever investment in the cold sweet stuff. It already has a 17 per cent share of the world market, worth a cool pound;3.6 billion, but is handing pound;71 million to its marketing and development staff to persuade us that we should eat more Heart brand products. (Unilever owns Wall’s, whose logo is a heart.

Presumably customers are supposed to think Cornetto, not coronary.) Ninety Cool bars are opening across Europe, the prototype van will be on tour and there will be a massive dance competition. People will also be able to buy - and dribble their unwrapped impulse product down - Heart bikinis, shorts, shirts and bags.

This is a far cry from the 1850s, when ordinary folk first chilled their tongues on frozen cream. Prior to then, it had only been for the nobs. And the biggest nob of all is thought to have had the first taste in Britain.

Charles II gave a banquet in 1671 at which he and his very poshest friends feasted on “one plate of white strawberries and one plate of iced cream”.

Everyone else watched. But not for long. The aristocracy were soon sending their servants out on wintry mornings in search of frozen pond water, which they stored in their stately-home ice houses. Ice was essential to the manufacturing process and in the 19th century men like Carlo Gatti, an Italian businessman in London, realised there was big money to be made.

Commercial harvesting began in Norway, Canada and America. After being shipped to the UK, the ice was transported in canal barges to massive storage pits. Some of these, built by Gatti near King’s Cross in London, have recently been opened to the public at the capital’s Canal Museum.

Gatti sold mainly to immigrant Italians who already had a reputation for good quality ice cream. Naples was where, in 1664, Europeans first sampled ices made with sweetened milk, and Neapolitan ice cream was named in recognition of their skills. “Ecco un poco,” they would shout: “Try a little.”

Nobody needed much persuading. Hokey pokeys, where the ice cream came wrapped in waxed paper, were all the rage. Also popular were penny licks, for which sellers filled up a small glass which was reused after the customer had licked it clean. The practice was banned in 1926 - Jnot surprisingly - on grounds of hygiene.

In the 1920s, Wall’s started to sell ice cream from tricycles. “Stop me and buy one,” was the slogan. And thousands did. By 1927, sales had reached pound;444,000, but during the Second World War sales fell and the tricycles were requisitioned for use in military installations. In 1947, Wall’s sold its 3,300 tricycles and spent the money on freezers in shops.

Since then, ice cream has become big business, clever science and sophisticated marketing. Sales men and women tell us that eating the stuff is one of our “favourite leisure pursuits” - Jnot just during the summer, but all the year round. The annual value of the UK ice cream market is already well over pound;1.25bn, but manufacturers believe we can be persuaded to eat more.

The latest idea is to let us have that ice-cream-van squirty stuff at home.

And there are moves afoot to broaden the appeal of savoury products - previously the preserve of posh chefs - with talk of curry and cheese flavours.

According to the UK Ice Cream Alliance, the Brits eat about eight litres each every year, much less than the Danes and the Swedes. No one matches the Americans, though, who get through a staggering 21 litres per person each year. Mind you, when it comes to ice cream and related deserts, the New Zealanders are the greediest. In 2000 they consumed 26.3 litres each.

The Chinese are the world’s second biggest producers, but only modest consumers - which is surprising because as far as anyone can tell they invented the stuff.

There are many myths and legends regarding the birth of ice cream. Some credit the Emperor Nero; others talk of Marco Polo. But the first real evidence comes from China’s Tang period (AD 618-907), according to the Ice Cream Alliance. Buffalo, cow and goat milk were heated together and fermented. This “yoghurt” was then thickened with flour and chilled before being served. The lucky recipient was King Tang of Shang, who had 94 ice-men on his staff of 2,300. He must also have had a liking for medicinal tastes as his dessert was flavoured with camphor.

These days, a camphor cone might be hard to track down, but garlic, sweetcorn and avocado are all on the menu. There are thousands of flavours and they are constantly changing. Posh ice-cream makers Ben amp; Jerry’s, now also owned by Unilever, list about 200 “dearly departed” tastes in their flavour “graveyard”. These include Bovinity Divinity, Aztec Harvest Coffee, Wavy Gravy, and Fudge Behaving Badly (that one for the UK market). And in the face of such riches what is the people’s favourite? Vanilla.

So just what is ice cream? Originally, it was pretty much what its name implies. All you needed to make a simple and delicious dessert was cream, sugar and fruit puree. This mixture would be poured into a metal pail sitting inside a wooden “hand-cranked” bucket filled with crushed ice and salt. As it froze, it would be stirred to prevent big ice crystals forming and making the mixture hard and coarse.

This would take about 30 minutes. Modern home ice-cream makers work on the same basic principle, although you can manage without them (see recipe).

But such homespun methods and simple ingredients are not for the multinationals. Tremendous effort has gone into making ice creams smoother, cheaper and longer lasting. Alas, the result is often little more than a tub of aerated margarine. Vegetable fat is used instead of cream and whipped up with sugar, water and air. Flavourings and colourings are added.

Then it is popped through the factory’s freezing machine. Provided it contains between 5 and 16 per cent fat, they can call it “ice cream”.

The nutritional content of cheaper ice creams, which are often targeted at young people, appals food writer Joanna Blythmann. In The Food Our Children Eat, she describes ice creams as: “extremely synthetic combinations of milk powder, chemically hardened vegetable fat, sugars and sweeteners, emulsifiers, colourings, flavourings, acidity regulators, all whipped up with lots of air. They tend to contain very little of anything that is beneficial.”

And some simply contain very little. Ice cream is sold by volume, not weight. This means that less scrupulous manufacturers can bulk out their products with air. American ice creams contain 40 to 60 per cent air, coyly called “overrun”. By US law, a gallon of ice cream must weigh at least 4.5 pounds. Homemade ice creams tend to weigh about seven to eight pounds a gallon. Ken Anderson, writing on the US website God’s Plan for Good Health, takes issue with additives. “The next time you’re tempted by a luscious-looking banana split,” he says, “think of it as a mixture of oil and nitrate solvent, antifreeze and lice killer, and you won’t find it so appetising.”

But it’s not all stomach-churning stuff. Many “premium” brands contain wholesome ingredients, even though you pay for them. There has been a growth in the number of small local producers who pride themselves on quality ice cream. The Food Commission, a pressure group for healthier eating, recommends that people “pay a lot and eat a little” when it comes to ice cream. Unilever might not agree.

Useful websites Canada’s University of Guelph www.foodsci.uoguelph.cadairyeduicecream Ice Cream Alliance www.ice-cream.org Ben amp; Jerry’s www.benjerry.com London Canal Museum www.canalmuseum.org.uk