The fourth generation of the RX luxury SUV from Lexus is the firm's most compelling effort to date. It's available with either a 3.5-litre V6 hybrid powertrain or a 2.0-litre four-cylinder turbocharged petrol engine.

The new car sits on a stiffened and extended all-steel platform that's a not inconsiderable 120mm longer than the old model. Half of that additional length is between the wheels so there should be no shortage of space.

The styling is much sleeker than the old model. Lexus claims that it provides substantial gains in refinement and efficiency. It also brings with it looks that will be reassuringly familiar to fans of the marque.

The grille dominates the front end because, well. it is huge. It echoes the angular, sharp-edged design of the rest of the exterior where, wheel arches aside, curves have been shunned in favour of bold lines, deep creases and sharp angles. It's a striking look that suits the big car well and, although some might find it a little fussy, I'm not among that number. I like it. A lot.

The cabin is beautifully put together. The upholstery is leather, while the switches, stalks and other controls feel robust and pleasantly slick. There are some hard plastics to be found, but you will have to poke around in places you wouldn't normally to find them.

The dash is dominated by the huge - 12.3in of colour LCD no less - widescreen multimedia display perched on top. It's operated via Lexus's proprietry mouse-style controller which can be a bit fiddly to operate, particularly while on the move, but it looks impressive.

There's a split-screen mode which assigns a third of the screen to a second function.

The leather-bound steering wheel feels particularly pleasant to wrap your hands around. It's electrically adjustable, as are the (heated and ventilated) supremely comfortable and supportive seats. It was easy to find the ideal driving position from which to enjoy the excellent, lofty, vantage point.

The sloping roofline does impact on headroom in the rear but there should be no complaints about legroom.

The RX is available with either a turbocharged petrol or V6 hybrid power plant and it was the latter fitted to my test car.

As is the norm in a hybrid, you're greeted with silence when you press the starter button and, as long as you show a restrained right foot, it will stay that way as you move off. Electric propulsion is good for a couple of miles, providing the RX with excellent efficiency in urban surroundings.

The suspension is comfort-orientated which makes for supremely relaxed long hauls - or short ones if you're just nipping to the supermarket - but that soft set-up means tight and twisty roads have to be approached with some caution.

The RX will turn in sharply enough, the steering is nice and precise, but the pronounced body roll means that there's a lot of mass shifting around on the springs, draining confidence and slowing progress.

The RX is equipped with a CVT box which, given the car's predilection for smooth, unruffled progress, proves to be an ideal companion. It's quiet inside too, with very little wind or road noise permeating the cabin, even at motorway speeds.

It's on the motorways, however, where you'll notice your fuel economy taking a bit of a hit and find out just how ambitious the official figures really are. However, owners will benefit from favourable BIK charge thanks to comparatively low emissions.

The RX is not a cheap car, by any measure, especially in Luxury trim but it's loaded with kit, including a 15-speaker Mark Levinson audio system, wireless charging plate and adaptive cruise control as well as a host of safety features and driving aids, but there are cheaper alternatives that are just as well specced.

It is, however, incredibly comfortable, beautifully engineered, and like nothing else on the road. It's also available in brown.

Lexus RX450h Luxury

Price: £57,995

As tested: £59,995

Engine: 3.5-litre V6

Transmission: Electric CVT

Max power (engine): 259bhp

Max power (motor): 335bhp

Max speed: 124mph

Acceleration (0-62mph): 7.7sec

Urban: 51.4mpg

Extra urban: 51.4mpg

Combined: 51.4mpg

Emissions (CO2): 127g/km

For more information visit www.lexus.co.uk