The Defender Octa is the most extreme, powerful and capable variant of the 4x4 that Land Rover has yet produced, complete with a spec sheet that reflects its top-end £158,000 price.

Limited to 1070 examples, the new flagship Defender is available in the 110 body shape only and is a way of showcasing the peak capabilities of the brand.

“This is a Defender on steroids – the pinnacle,” said Defender and Discovery brand boss Mark Cameron. “Nothing else on sale feels like this.”

The first model from the new Octa sub-brand for special-edition Defenders is powered by the same 4.4-litre BMW-derived V8 as the Range Rover, but it has been ramped up to 626bhp and 590lb ft to rival the Mercedes-AMG G63.

That’s enough muscle to push the 2510kg SUV from 0-60mph in a supercar-baiting 3.8sec and all the way to a top speed of 155mph.

This puts it close to the Range Rover Sport SV for outright pace and dwarfs the standard Defender V8, which uses JLR’s older supercharged unit, by 108bhp.

But despite its prodigious on-road performance, the focus for the Octa is more on providing greater levels of off-road ability than any Land Rover to date.

To prove its durability and duality, engineers put the Octa through 13,960 tests and clocked up 683,508 miles in challenging and wildly varying conditions all around the world.

These included sand dunes in Dubai, snow and ice circuits in Sweden, on track at the Nürburgring and at the unforgiving Dakar Rally proving ground in the south of France.

JLR said it had to create a bespoke and highly varied test programme for the Octa given its wide-reaching breadth of capability, trialling new heights of “capability and robustness that have never been explored before”.

The intention was “to demonstrate it could push the boundaries of what a Defender can do”, without compromising on-road drivability or comfort, Jamal Hameedi, boss of JLR’s SVO division for special vehicles, told Autocar.

“No one has ever made a car that is as good on road as it is off road, with no compromise to go between the two,” he said. “This was a white-sheet vehicle… to create something that is as fun on the Stelvio Pass as it is on a rally stage.”

The key to this flexibility is the Octa’s highly advanced chassis set-up. The model is fitted with the 6D Dynamics suspension system from the Range Rover Sport SV, which hydraulically links the dampers front to rear and side to side to actively keep the cabin as stable as possible without the need for a physical anti-roll bar.

New front and rear bumpers increase the Defender’s maximum approach angle to 40deg (up from 37.5deg), departure angle to 42deg (from 40deg) and breakover angle to 29deg (from 27.9deg). The ride height has risen by 28mm over the benchmarked Defender 110 V8, with a maximum ground clearance of 319mm.

The wading depth has also improved by 100mm to one metre. The maximum articulation has significantly increased to 569mm from the standard 110’s 430mm, too.

In addition, the Octa features longer and tougher wishbones, beefed-up underbody protection and the quickest steering rack of any Defender yet to improve reaction times over extreme terrain and on the track.

As well as the standard drive modes, the flagship is equipped with a new Octa setting, which in addition to priming the SUV for the toughest trails has a dedicated off-road launch mode built in.

To get the most out of the flagship SUV, engineers have created a bespoke off-road tyre. Fitted to specially designed 20in rims, the Advanced All-Terrain rubber was developed in partnership with Goodyear and features a bespoke tread pattern. It is limited to a 99mph top speed.

“There’s so many little stories where we refused to compromise – that was the mentality – and that new tyre is one of them,” said Hameedi. “Traditionally, an off-roader would say: ‘Oh, I want an 18in wheel with a tall sidewall for puncture resistance.’

But then that ruins your on-road steering and handling, and you can’t fit proper brakes. “So we said: ‘No, we need proper on-road steering and handling, a lot of lateral stiffness, big brakes [400mm discs with Brembo calipers] because of the power, and to be puncture resistant.’ But no one has all that. So we had to invent a tyre from scratch.”

There is, though, a less extreme alternative that splits the difference between the bespoke All-Terrains and the standard, road-focused all-seasons, with a top speed of 130mph.

As well as flared arches, exclusive alloy wheels and a loftier ride, the Octa stands out from the standard Defender with a new, more open grille design and diamond Octa badge on its C-pillar.

All Octa models feature a contrasting gloss black roof and tailgate. Inside, it gets new performance seats with a 3D-knit texture, an integrated headrest and a seamless finish, something that will be made available in other JLR vehicles soon.

The Octa also features the top-rung 11.4in infotainment screen, a centre console fridge and Burnt Sienna semi-aniline leather as standard.

Priced from £145,300, the limited-run Octa is not only a crucial source of revenue generation for future product development, particularly the electrification of all four JLR brands, but it also shows how far the Defender brand can be taken, JLR UK boss Patrick McGillycuddy told Autocar.

He said: “The capability and breadth of the brand is immense, as is now the capability and breadth of the product. “We limit the volume to give these cars a special appeal, but they’ve also got to be incredible things – incredibly well engineered.”

The most hardcore variant will be the launch-spec £158,000 Year One edition, which has the top-rung tyres, 20in wheels, a roof box and a rear ladder. It is marked out from the standard Octa by carbonfibre detailing, Faroe Green paint and khaki interior features.

The more road-focused Octa (half of owners never take their Defenders off the Tarmac) comes with 22in alloys with all-season tyres and retractable side steps.

Special colours, such as Petra Copper, Faroe Green, Carpathian Grey and Charente Grey, will also be introduced by the Octa. Matt finishes, which include a protective film, of all colours are available too. These colours will later filter into the core Defender range.

The Octa will make its dynamic debut at next week’s Goodwood Festival of Speed. Order books will open on 31 July and the first deliveries will begin later this year.

Q&A with Mark Cameron, managing director Defender and Discovery 

How does JLR see the Defender brand?

“If we look at how we’re carving up what used to be the Land Rover brand, Defender owns most of that, especially that go-anywhere, epic adventure side. So it’s almost like you’re translating what people know is Land Rover to now being Defender.

“That includes the Land Rover-branded experiences we offer too that will in time transition to Defender – and we will use that to show customers what their cars are really capable of.”

What’s the brand direction for Defender?

“It’s going to be even more bulletproof, more robust, more durable, more ‘kick it and it still comes back for more’. We will of course be pushing forward with electric, too, and what that means for the brand, as well as a refresh for the current model to keep that fresh.”

How do you differentiate Defender from Range Rover?

“It’s quite a task. At the moment, we do have a shared retail footprint, but by having a really clear definition of what one brand is and what another is, and designing and engineering to the brief, you ultimately start moving to the separation.

“In short, Defender is ‘tough luxury’ and Range Rover is ‘refined luxury’. Although your delivery of what luxury is is totally different, it doesn’t mean you can’t charge a similar price.”

What’s your typical customer?

“These customers have a bit of a dream for something different. Yes, their day-today may be a school run or city commute, but they have this desire to be somewhere else, to go to their Everest – doing something epic one day.

“And, according to our data, at least 50% of owners take their cars off road at least once a month.”