It was the 1956 Suez crisis that launched the Mini on an unsuspecting world. Not immediately, of course - the motor industry's first response to the oil shortage was a series of so-called "bubble cars". These were certainly energy-efficient, but when the first Mini rolled off the assembly line in August 1959, it had something they lacked. It was a car you could drive while retaining your self-respect.

Three years earlier, in the quest for something acceptable, the British Motor Corporation turned to the man who had already given it the Morris Minor. If the oil crisis was the mother of the Mini's invention, Alec Issigonis was its father. Anglo-Greek (though born in Turkey), he was a man who liked to get his own way. And he did: when the new car emerged in prototype in 1957, it was all his own work, idiosyncrasies included.

A French philosopher has compared the modern car to a cathedral; but on a scale of ecclesiastical builings, the Mini was more of a Gospel hall. At a retail price of £496 (£100 cheaper than the Ford Anglia), it had to be Spartan - in the first models, the door was opened by a primitive string-pull device, to save space and money. But some of the minimalism reflected the inventor's own prejudices. He reportedly hated listening to the radio while driving, so the new car had no radio, and nowhere to put one.

The Mini's innovations included front-wheel drive, gearbox under the engine, rubber-cone suspension and tiny, 10-inch wheels. But the sheer verve and the road-handling for which it would become legendary was still a surprise. The car critics were wowed. The Daily Herald gave it a two-day "bashing" on army testing grounds before the critic ". . . gave up. I couldn't fault the machine". The Daily Mail predicted a "motoring revolution".

And yet it would be more than a decade before sales really took off. Indeed, it probably took the invention of a sporting version - the Mini Cooper - in 1961 to secure the car's legend, and this is where an Irishman took centre-stage in the success story.

By driving a Cooper to victory in the 1964 Monte Carlo rally, Paddy Hopkirk wiped the eye of such giants as Mercedes, Ford and Citroen, who were spending millions every year trying to win the event. And from his marketing business headquarters in Buckinghamshire yesterday, he was still excited about it. Thirty-one years old at the time, he arrived in Monte Carlo not knowing he'd won. "So I just went to bed, and this journalist woke me in the middle of the night with the news - he had inside information. There was still one final, special stage around the streets of Monte Carlo, but I was so far ahead I couldn't be caught."

One of the peculiarities of the Monte Carlo event was that each competitor had to drive to the start-point proper (in Grenoble) from a given European city, within a given time-limit. Paddy's city was Minsk - an adventure in itself.

The temperature there was 40 Celsius Celsius and - since everything in the car froze, including the oil - it had to be towed around a city square on the morning of departure, allowing locals to boast about the superiority of Soviet technology. When he did get going, there were other hazards. "I had four snow tyres in a bag in the back seat, and it looked like a body. Crossing the borders of Czecholoslovakia, this soldier started sticking his bayonet into the bag, and I had to plead with him not to puncture my tyres."

Belfast-born, but Clongowes and Trinity-educated, Hopkirk says the team's resources were modest by comparison with the bigger companies, but the car was perfectly suited to the course, with its narrow, twisting roads. "With all the snow, it was like a Cresta Run in parts, and the Mini's four-wheel drive - with the weight over the wheels - was ideal. It was a bloody good little performer".

If Hopkirk was the cutting edge, hundreds of thousands of less accomplished drivers were now following. The millionth Mini was sold in 1965, the second millionth in 1969 and the three million mark was passed in 1972.

By then, the car's status as a 1960s style-icon had been enshrined for posterity in the Michael Caine film, The Italian Job. But ordinary owners were developing an affection for the car which had nothing to do with its rallying talent or film-star looks.

Margaret Dowsett, a teacher in Dublin's High School, was a "serial" Mini-owner until she recently succumbed to the comforts of something bigger. She bought her first one for £100 20 years ago (it was already ancient at the time) and learned to drive in it before selling it for £50.

She also recalls once trying to "edge" past a milk float in another Mini and seeing the wing of the car peeled away, "as if by a can opener . . . one of my students who was very good at art wanted to paint a zipper on it".

Many similar stories will have been exchanged over the June bank holiday weekend, when the Irish Mini Owners Club celebrated the 40th anniversary with a Mizen-to-Malin drive - 59 cars (some of them up to 30 years old) participating.

"The aim was to get them all there within a single day and, although one blew a gasket, we made it," says club president, Jocelyn Kelly - who, along with her husband Paul (founder of the club and of a business in Drumcondra dedicated to Mini repair) is the proud owner of no fewer than five Minis.

But with an Irish MOT test on the way, leaded petrol soon to disappear from forecourts, as well as the general advance of safety and environmental standards, she concedes that the on-road Mini population is rapidly thinning.

The cars are still being made at the (now BMW-owned) Rover plant in Longbridge, near Birmingham, and Japan is buying them at a rate of 8,000 a year. The Mini Cooper is still in demand here, albeit selling at a rate of "about one a month," in Dublin's Stuarts Garages, according to sales manager Sam Power.

Twenty-five years ago when he started, salesmen were putting them through their hands at a rate of "one and a half a day," bought by everyone from learner drivers to elderly people who liked the easy parking. These days, the buyers are "people who want something different," and the basic package is £11,100, rising to £12,600 for extras like leather seats, wide sports wheels and spotlights.

But time is running out for the old car. Late next year, the Mini 2000 will be unveiled by BMW. An attempt to marry modern safety and environmental standards to the traditions of the brand, it will be a foot and a half longer and quite a bit more expensive, at somewhere between £12,000-£13,000 sterling. The engines will be made in Brazil, although the cars will still be built at Longbridge; and BMW/Rover hope to sell up to 150,000 a year.

In the meantime, Mini fanatics are adopting a wait-and-see policy. "The jury's still out on the new car," says Jocelyn Kelly. "We've been told that it's true to the original - that the cheekiness is still there. But we haven't made up our minds if it's one of our own yet."