When prototypes of the Morris Mini Minor and its almost identical twin, the Austin Seven, were first put on the road, the British Motor Corporation hit an unforeseen snag: the car was just too fast. With a lusty 948cc A-Series engine nestling under the disguised bonnet, Britain’s front-wheel-drive secret weapon would clock more than 90mph. This was considered excessive in a world where most traffic struggled to do 50mph, so the new baby had to be reined in.

Part of the solution was the accidental side-effect of turning the entire engine back to front to stop the exposed carburettor from icing up¿ A car that did 90mph backwards would definitely cause alarm, so an extra gear then needed to be slotted into the transmission to reverse the drive, craftily losing about 4 per cent of the surplus power (and adding that characteristic whine). This didn’t quite do the trick, so the capacity was then reduced by 100cc, resulting in a production Mini capable of a nice, safe 70mph.

This is all a bit ironic now, because virtually everyone else in the world promptly tried to make the little marvel go faster. And nearly half a century later they’re still trying, even though there are so many easier routes to speed, simply by starting from a different place.

Some of the most unfeasibly fast Minis produced in recent years have been built by Z Cars, based in East Yorkshire. The company was founded by Chris Allanson, who somehow managed to combine working as a policeman (hence the business’s name) with constructing a series of extremely rapid cars for au-tograss racing. Driving his own creations, he became British champion in this closely fought branch of motor sport.

Chris was then asked to build similar cars for other people, the USP being that they were powered by motorcycle engines¿ two motorcycle engines, driving through two gearboxes and clutches. After proving how well the idea worked on grass, twin-engined road cars in the Lotus 7 mould were next on the agenda. Capable of 0-60mph in less than three seconds, the 4WD Z Cars Tiger set acceleration records.

Point proved, the emphasis shifted towards malevolent Minis. In 2002, a 340bhp, Kawasaki-engined “Twini” was put together for a customer. Interestingly, this idea had a precedent, because in the 1960s John Cooper built a twin-engine Mini for the BMC rally team. In the hands of John Whitmore it worked well, but development stopped after one car was involved in a serious road accident.

Although the Kawasaki Twini wasroad-legal, itwas hardly ideal for everyd transport. But the project created an enormous amount of interest, prompting him to design a lightweight, single-bike-engine Mini. Such has been the response that PC Allanson took early retirement from the police and Z Cars has expanded rapidly, to the point where it’s now one of Britain’s largest homegrown manufacturers.

I’ve been lucky enough to try several of the bike-engined creations, such as the first record-breaking Tiger and the Twini. Any initial reservations I had about using motorcycle power units in cars were soon dispelled. As nearly was my breakfast: the Twini in particular has to be seen and heard to be believed.

For those who still think cars should have car engines, the latest Z-machine uses a m i d mounted Honda V-TEC power unit. Plainly, if a Civic Type R is fast, the same engine in a car weighing barely half as much will be breathtaking. Subtly tweaked to around 250bhp, 0-60mph in 3.5 seconds and 153mph are the figures.

Going fast in a straight line is one thing, but there’s far more to it than that. Like everything in the Mini, the suspension was designed with compactness in mind, and it struggles to cope with wide wheels and rampant power. So the whole lot is thrown away.

The engine is installed in a sub-frame incorporating a semi-tailing arm set-up, while the front end is replaced by a beautifully crafted wishbone and rocker-arm suspension, with rose-joint linkages and adjustable spring/dampers.

The end result is astonishing. There are faster cars, but not many, and I doubt if any are as thrilling to drive. Although having an engine instead of back seats and a radiator instead of boot space does lower the practicality factor somewhat, compared with a Caterham or Westfield the Z-Mini oozes convenience. It’s very easy to drive, economical and has surprising ride comfort, thanks to the sophisticated suspension.

Remarkably, only four gears are needed.

First is actually third in the Honda ’box, and is good for more than 70mph, which should amuse the magistrates’ court.

Apart from the steel-shelled model, Z Cars also offers the Monte Carlo, which looks like a Mini but is really a space-frame chassis clothed in a fibreglass replica body-shell. It weighs even less and comes with up to 400bhp, so please don’t ask if it’s fast. What better way to celebrate what would have been Sir Alec Issigonis’s 100th birthday?

Z Cars, 01964 527 725, www.zcars.org.uk . Price: depending on specification, from about £5,000 for the basic kit to build a mid-engined car, and in the region of £25,000 for turn-key cars.