Stephen Bayley: Never frivolous, a British classic that has always been a triumph of design

The original Land Rover is one of the all-time classic cars. Typically for a British product, it was also something of a glorious lash-up and compromise (although an inspired one). By the time it is replaced in 2015, the Land Rover will have been in production for nearly 70 years, a figure that exceeds automobilia's distinguished gerontocracy of the Model-T Ford, the Volkswagen, Mini and Porsche 911. It is an absolute and unchallenged masterpiece of industrial design.

Land Rover began when Maurice Wilks, a member of the family which owned Rover, acquired an Army surplus American Jeep for use on his Anglesey farm. Wilks was both an inspired businessman and a dedicated engineer, one of the people who developed the Whittle jet engine. He felt he could improve on the crude Jeep. He did and his idea debuted at the 1948 Amsterdam Motor Show. The world loved it. No "designer" was involved. Certainly, Wilks had ideas to improve the Jeep's crude four-wheel-drive transmission, but while his creation is used and admired by farmers and soldiers everywhere for its astonishing ability to conquer swamps, deserts, mud, rubble, slime and climb walls, Land Rover's fundamental appeal is based not in functionality, but in semantics.

It is a near-perfect geometrical composition, using only straight lines and very simple radii. There are no frivolous decorations nor anything not determined by purpose – but far from being banal and utilitarian, the Land Rover is evocative and delightful. Something about its unashamed honesty speaks very directly to our emotions. All the associations are positive: never has a piece of agricultural and military equipment been so winsomely friendly.

But time's winged chariot has overtaken four-wheel-drive: the old Land Rover is clumsy and expensive to manufacture and has difficulty meeting modern safety criteria. Designing its successor, now known as the Defender, is the job of Gerry McGovern, who has already transformed the Range Rover into a global luxury product and, with the new Evoque, realised the vast reserves of valuable image capital residing in the idea of "Land Rover".

The architecture of McGovern's new Defender respects the geometry of the original, but expands simple co-ordinates into an evocative design language. Right now it is being tested on you and me. If it works, this car will still be manufactured in the third millennium.