Four decades ago today, the nation was slightly startled by the arrival of a dramatic-looking new slice of family car. A wedge-shaped slice, which had come from the by now rather pedestrian Austin-Morris division of British Leyland.

The new 18-22 Series was launched on March 26, 1975, and earlier I attended a modest ceremony to mark the fact at the place of its birth, at what is now BMW’s Mini factory on the edge of Oxford.

Strictly speaking, we were told - by a Mini factory guide who worked there at the time - that the 18-22 was manufactured on the other side of a bypass on land now occupied by a gym, an Audi dealer and a science park, but the 18-22’s body was made on the part of the site from where Minis emerge today.

In case the 18-22 Series doesn’t sound familiar to you, you may remember this car as the Princess, or following a demotion and a sex-change, the Ambassador. The Princess is what it became after nine months, when BL decided to rationalise the original Austin, Morris and Wolseley versions under this one nameplate.

The Princess tends to be lumped with the Morris Marina and Austin Allegro as an example of one of the worst cars produced by Britain’s troubled motor industry in the 1970s, but the 'wedge' differed from this infamous pair in that it was actually rather good.

During 1977, this very magazine rated the six-cylinder 2200 HLS as the best car it had tested that year, although this was partly the slightly embarrassing result of an admirably obtuse scoring system used by the mag at the time.

Nevertheless, the Princess was an entirely credible rival to the recently released Citroen CX and made Ford’s Granada look like a throwback. Its strengths were cabin space, ride comfort, interior fittings, road holding and refinement. Oh, and its Tomorrow’s World wedginess. But by the time it had mutated into a Princess, a number of weaknesses had emerged.

Austin Morris touted the 18-22 Series as ‘the car that’s got it all together’, an ad line that was just asking for trouble, which duly arrived in the slightly alarming form of failing rear suspension mountings and an appetite for driveshafts that would result in the six-cylinder engine undergoing a minor relocation within its engine bay. Hard to imagine a mod like that being pursued today.

The 10-or-so Princesses lining up on this windy March morning - there would have been more, including my own, but several are works-in-progress - were joined by the car’s key creator Harris Mann, who designed this, the Marina, the Allegro and the Triumph TR7. 

It was a creative record that made him (in)famous at the time, but as he’ll quietly point out with the aid of his original sketches, his intentions for the Allegro and TR7 were somewhat different from the end result.

Of the quartet, he says, the Princess is his favourite because it most closely replicates his original vision. "We wanted to take the company into the modern age," he says, showing a picture of the 18-22 parked beside its frumpy Austin 1800 predecessor. The shot was taken in 1971, four years before the 18-22’s launch, and the clay model looked ready to fire British Leyland 20 years into the future.

But as always with BL cars of the 1970s, the 18-22 was haunted by the issues of the past, its enthusiastic reception (three-month waiting lists grew within weeks) was soon savaged by strikes and quality troubles from which it never recovered.

"They took too long to sort them out," says Mann, looking slightly frustrated with BL’s management even today. Examine the fine array of design sketches he has brought, some shown here, and you can understand why.