That great steel and aluminium beast, the Land Rover Defender, and its ancestors have been clanging and clunking their way off the production line at Solihull since 1948. Born in postwar rationing, the Defender feels as quintessentially British as the Queen, Churchill or Bond, among the other national icons who have been plonked atop its unbending chassis.

Orders have boomed of late, and the 2 millionth Defender will be auctioned off at Bonhams in London next week, probably for the price of a luxury sports car. But the model that has served adventurers, soldiers, farmers and generations of enthusiasts is almost done: overtaken at last by time, technology and legislation.

The cold truth of the business is that the manufacturer, Jaguar Land Rover, is now owned by Indian multinational Tata, and the world has moved on. In early 2016, production of the Defender will cease at its West Midlands home.

Queen Elizabeth II in a Land Rover in Windsor, Berkshire, 1987. Photograph: Georges DeKeerle/Getty Images

Eric Davis worked on the original production line of what was then the Land Rover Series I. Now aged 90, he has returned for a visit and looks on intently as his modern successor attaches the bolts to a panel of a Defender. Davis, who had spent three years in service in Burma during and after the second world war, landed a job as a wing fitter at the factory through his brother, who had joined from making Spitfires nearby.

“it’s much easier now,” he laughs, “it used to be all.” He mimics the rapid arm movements of someone tightening bolts with a spanner. Now, there’s a pneumatic fastener.

Land Rovers have been built there ever since: the operation has evolved and expanded, but the Defender (as it was rebranded in 1990) is, if not exactly hand-crafted, made with a far bigger human input than found in most modern car production lines. In places, robots swing door panels around to spot-weld with pinpoint accuracy; but a few metres away, a section of the factory still runs as it did 67 years ago, Davis confirms.

“Building the face of one of the world’s most iconic vehicles - this production line has never changed,” says Michael Bishop, a Land Rover historian who leads tours of the line.

After the Defender’s body is assembled, it takes a day to treat with 185C baths and electrolysis in the paint shop. Photograph: Christopher Thomond/The Guardian

He holds up a metal part that has been in every vehicle from one to 2m, a “stiffener top” for the rear wheel well. The engines, gearboxes and even the doors now have a complexity that sees them constructed elsewhere, but the transformation on this line of the dull sheen of aluminium parts into a moving vehicle at the other end is still something to behold. Not bad for what Bishop characterises as a giant meccano set.

After the body is assembled, it takes a day to treat with 185C baths and electrolysis in the paint shop, before the fitted-out Defender emerges on day three, in a succession of four-minute stages along the assembly line where around 500 people work. Every vehicle is built to order, from a vast array of permutations of bodies and bases.

Model Land Rover Defenders at Land Rover Experience tour in Solihull. Photograph: Christopher Thomond/The Guardian

“It’s hard to find two the same, even normally. And all these are limited editions,” says John Carroll, the editor of Classic Land Rover, at the Solihull line. The vehicles made during a ramped-up final year of production in Solihull include tributes to the HUE 166, the original Series I model whose Birmingham area number plate devotees all recognise, with Defenders painted in that original shade of RAF surplus green.

Its conception owed much to the war: the Rover firm had grown from a Victorian sewing machine manufacturer via bicycles to carmaking, and moved to Solihull – a camouflaged site built to manufacture aeroplanes in the war – in 1945 after its Coventry home was bombed. Rover’s chief engineer, Maurice Wilks, had been running a Jeep – the US army’s second world war workhorse – on his farm at Anglesey and was inspired to go one step beyond, famously sketching out the design for his new vehicle on the island’s sands.

With a four-wheel drive, a light aluminium body, bench seats and canvas roofs, the Land Rover was said to be like a Jeep but better. To mark the first year of production, children of staff were invited to the Solihull factory celebrations, which included demonstrations of the new Land Rover driving at a 30 degree sideways tilt on the test track. As the adults climbed aboard, Rover spotted a winner: the adventurous test drive became a marketing device that persists to this day.

The iconic vehicle has been produced at the Sohilull site since 1948 but the company will cease production next month. Photograph: Christopher Thomond/The Guardian

An exhibition in the heart of the Defender production line compiles a small history of owners’ and enthusiasts’ testimonies, from the vehicles used in pioneering Royal Geographical Expeditions, a battered Series I handed down from first owner to granddaughter, and more than one Land Rover used as couples’ official wedding cars. The manufacturer estimates that 66% of all those ever built are still on the road.

So given the longevity and the passion it inspires, what has sealed its demise? Partly, changes in legislation that made some of its distinctive features outmoded, if not downright illegal. Side-facing seats in the back were outlawed by EU legislation after 2007, and changing standards, in fuel consumption and emissions to crash tests, made more and more facets of the Defender unviable. Once no longer compliant for sale in the US, the Defender’s prospects in other markets were severely curtailed.

The harsher truth is that even its admirers have started to turn away, no longer as forgiving of its faults. The reviews are telling: while the readers of What Car? still proclaim their passion for the Defenders they own, the professionals have had enough: a one-star verdict, “woeful” on safety, “loud” and “a horrible ride”. It sums up: “Off-road, very little can touch it. On-road, there’s very little to recommend it.”

The Defender’s interior is fitted at the Solihull plant. Photograph: Christopher Thomond/The Guardian

While the nostalgia-fest has stoked strong sales throughout the last year of production, the manufacturers clearly had to act. A Jaguar Land Rover spokeswoman says: “As loved and iconic as it was, it needs a full overhaul. As a business model it needs to advance. But the story of Defender will continue.”

A next generation model of the Defender is expected to be unveiled in the next two years – one whose stature is more akin to the modern 4x4s on the road. Marketing departments of the future may be keen to stress its heritage to certain buyers, likely the Brits. But Land Rover concedes that the clear lineage of the current Defender from the Series I of a very different postwar Britain will be gone. And whatever its future shape, no one will claim it to be handmade in Britain.

• This article was amended on 11 December 2015. An earlier version gave the year 1983 where 1990 was meant.