Britain’s classrooms are being invaded by aliens. Tamagotchi - “the tiny pet from cyberspace” - is the toy of the moment among a small but growing number of children. While schools in the past could easily instruct pupils to leave their Pogs or Power Rangers at home, the Tamagotchi needs regular attention throughout the day. Neglect it and the virtual pet will become ill, or ugly, or even die.

Tamagotchi (“tiny, pretty egg”) comes from Japan where millions of otherwise well-adjusted adults are addicted. Businessmen, it is said, interrupt meetings to clean out their pets’ virtual cages, to feed the creature a snack or give it a cyber telling-off. The size of a pocket calculator, it’s housed in a small egg-shaped casing with a small square screen where its tummy might be. Retailing at Pounds 9.99 upwards, it hatches, paces up and down, laughs, cries, munches and does poos, and is rare as hens’ teeth - as an older generation reared on furry or feathered creatures might say.

In search of the rarity shortly before my son’s 10th birthday, I found myself in the carpark of a well-known toyshop, soon after seven on a Saturday morning. The queue was already well-established and by 7.30am, 53 people had gathered, equipped with picnic chairs, cheese sandwiches and books.

At the head of the line was 22-year-old Kenneth Chung, from China, who had three Tamagotchis already but wanted a white one - the most unusual of the four colours made. Next were 13-year-old Adam Edelshain and his sister Laura, 11, with Dad, a business studies lecturer.

These two already have a hamster. Why do they want a Tamagotchi? “You don’t have to clean its cage out, it won’t bite and you can make them relive, ” says Laura, practical in the way girls are. “And you can take them around anywhere. ” Except into her school, Sarum Hall in north London, where they are banned. Adam Edelshain was in the queue the week before for a Tamagotchi for his younger sister and has come back for one for himself. Are they popular in his school? “Not yet. But they will be.”

The toy has more in common with computer games than pets. But the manufacturers claim it teaches children nurturing skills. Various commands activated by the three tiny buttons mean the owners can feed the pet a snack or a meal, play a game with it, clean the cage, shout at it or turn the lights out for it to sleep. The pet registers hunger or satiety and happiness - or the lack of it - through a row of full or empty hearts, and can become ill and die for various reasons. You can make it happy by giving it a snack - but give it too many and it puts on weight, bursts even. The other way to make it happy is to play a repetitive game with it.

By 7.45, people are arriving in droves. About half are Japanese. One Dad paces the carpark, his mobile glued to his ear, a woman writes her diary sitting on a plastic crate. The queue is quiet and good-tempered, with only the children showing signs of excitement. The toyshop staff look out rather edgily from behind the plate glass. Last Saturday, according to someone in the queue, there were ugly scenes when those at the back didn’t get a toy.

Tamagotchi is made by Bandai, who expect to sell more than one million of the toys in the UK by the end of the year. Spokeswoman Sara Stewart says the company sells more than one million a month in Japan. Does Bandai not fear that the toys will interrupt children’s education, beeping for snacks and pining for lack of attention during double maths? “That’s a bit of a difficult question, ” she says. But on reflection, she believes not. “Children can turn the sound off, and they don’t require immediate attention. It should fit in with breaks and lunchtimes.”

At Brookland Junior School in affluent Hampstead Garden Suburb, north London, I ask headteacher Grainne O’Reilly-Askew, if she has heard of them. “Oh gosh, yes,” she says. “They are in my school with a vengeance.” Not causing any problems, then? “Children know they’re not allowed to wear them around their necks, for health and safety reasons. They put their names on them and take responsibility for them and in school they are quite unobtrusive.”

There is a less benign view from the staffroom of the 760-pupil Japanese School in Acton, west London. “The school rule is that they don’t bring anything which is not linked with subjects,” says Shizue Sunaga, head of English. “Some of them come by school bus and have long journeys, and they can play with them then. But not at breaktimes.” Two colleagues chip in from the background with a view that the game gives technology the upper hand and makes children introverted. “Tamagotchi’s popularity is going down at home,” says another, damningly.

But not in Blighty. By 8.30 there are more than 180 people in a line which snakes (remember them?) around the carpark. The queue now has that anxious competitive feeling associated with the meeting of desire and shortage. The shop limits the toys to one per customer, and issues tickets before opening time. They have been getting enquiries at about the rate of 10 an hour, says an employee. Since the launch on May 9, they have sold about 1,000. He doesn’t like to give his name but he’s 28, and hasn’t got one. “I just think if you can’t have a real pet why get a little computerised one.”

All the major shops are facing the same shortage. Harrods has stopped taking names as it has 200 telephone orders already. Selfridges is sold out and advises ringing early next week. “It’s huge,” says the toy department manager. “Boys and girls, accountants and solicitors in the City, and the young trendy clubber. They’re flying out of the store.” The toy is popular amongst art students, he says - he’s heard that a creche has been set up for them at St Martin’s College of Art.

By 9am - opening time - more than 200 people are lined up for the estimated 120 toys which arrive in one order. When the doors open, customers enter at a run, and the tills ring. By 9.15 it’s all over. Most people leave with a cyber pet, some are disappointed. My son is one of the lucky ones, and an hour after hatching his Tamagotchi he seems to have grasped at least some of the complexities of caring for a newborn.

“It’s always hungry and it’s never happy,” he says. “If you shout at it, it gets confused then it gets unhappy and you have to give it a snack to make it happy. But then it puts on weight. ” He’s enjoying the responsibility, but I’m not so sure. I’m not allowing him to take it to school, and so have landed myself a new job as virtual babysitter. I got his brother one too. Must rush.