The third generation of the Lexus RX SUV pledges class-leading power, more miles per gallon and a £105 annual car tax bill.

These impressive credentials are down to development of the Japanese manufacturer's Congestion Charge-beating Lexus Hybrid Drive technology: the part petrol and part electric hybrid powertrain introduced on the current model.

This promises a package of:

• Power output up to 295bhp
• CO2 emissions down to 148g/km
• Average fuel economy of 44.8mpg

Add improved driving dynamics for a more engaging time behind the wheel thanks to substantial suspension updates and it sounds like Lexus has a winner.

The RX gets bigger

The new RX is longer, wider and higher than its predecessor to the tune of 15mm, 40mm and 25mm respectively.

Subtle design developments are informed by the LF-Xh concept crossover (or in Lexus design speak: coupling elegance with muscular looks) while equally discreet improvements, including reductions in panel gaps, contribute to a sleeker car.

Increased dimensions mean noticeably more space inside for passengers in the already roomy SUV while on the luxury side of things seats can now be adjusted for cushion length.

The interior has undergone substantial revisions with the dash split between self-explanatory display and operation zones, aimed to present drivers with easy-to-use controls.

A head-up display with satnav directions, speed and adaptive cruise control information appearing in the driver's line of sight (and making sure their eyes stay on the road) is a welcome development. However, a new Remote Touch system with computer mouse style control located between the driver and front passenger (the Lexus equivalent of BMW’s iDrive) is a nice idea in theory but might take some time behind the wheel to get used to (clicking “enter” on the side of the mouse control rather than the top weren’t immediately intuitive).

Lexus has reduced cabin noise from the engine, road and wind. Other “luxury” touches include dual speed windows (which means they begin opening and finish closing slowly) while revised aircon means you can adjust the temperature higher and lower than you could in the outgoing model.

Revised hybrid technology

But the most substantial developments have occurred beyond the motorist's gaze. The main power source is still the V6 3.5-litre petrol engine from the original RX 350 supplemented by two electric motors operating in a series/parallel system.

There's a new power control unit, a revised combustion cycle, new systems to recover expended energy and an artifical intelligence gear shift system which improves gear selection by comparing the angle of the accelerator with the car's speed to identify whether the car is going up or downhill. Clever stuff, though we still found manually flicking the gear shift the most dynamic way through some twisty roads on the two-hour route.

Cheaper, faster motoring

This is supported by a total power output of 295bhp which enables the car to cover 0-62mph in 7.8 seconds and produce a top speed of 124mph. In practice this lends the car greater ability to overtake swiftly and safely with a satisfying squirt of the throttle.

The two electric motors help keep CO2 emissions down to 148g/km. By the time the car goes on sale this will place it in new car tax band F with an annual bill of £105. Fuel economy averages at just 44.8mpg and Lexus claims this return and those emissions are class-leading against the BMW X5 and Mercedes ML.

There are three driving modes to toggle between:

• EV: Exclusively electric motor-powered driving (for distances of up to 3km).
• ECO: Smooths out jerky driver acceleration input through the accelerator and gearbox for more fuel efficient motoring
• Snow: Adapts the car's capabilities for more demanding terrain and conditions.

There is also a choice of four ride heights thanks to the newly-engineered air suspension system offering better clearance or enabling shopping to be loaded into the 446 litre bootspace more easily.

Better through corners

There have also been substantial revisions to the driving dynamics which include lowering the petrol engine (and the centre of gravity), installing a new rear suspension (double wishbone replacing strut) revising the front suspension and introducing a stabiliser system said to reduce body roll through corners by up to 40 per cent compared to the outgoing model. The car also features a new, stiffer bodyshell.

We certainly found there was minimal roll through corners which we tackled at speed confidently. The car's ability to skirt across substantial potholes with minimal discomfort to the occupants impressed even more, with one particularly poorly-paved section of our trip dismissed with ease while we were bracing ourselves for a series of jolts. And, despite the increase in size, the RX retains the same 5.7m turning circle of its predecessor.

Safety features

Aside from head-up display, other safety features on the new RX include pre-crash safety devices with the car alerting the driver to a potential crash, supplementing driver braking inputs and ensuring headrest and safety belt optimisation prior to impact. The RX also has ten airbags, anti-lock Brakes, traction control, Vehicle Stability Control and Electronically Controlled Brakes as well as the increased stability of four wheel drive.

The Lexus RX 450h will be available in four trim levels SE, SE-I, SE-L and SE-L Premium. Key features of each level are listed below.

The new Lexus 450h sees the Japanese manufacturer move its SUV offering forward in a big way, responding to motorists’ financial and environmental concerns while improving the car's fun side with engaging driving dynamics and more power. It is available for orders from £41,600 and hits UK roads in July

Lexus RX 450h specifications

SE: leather upholstery, heated and electrically adjustable front seats, dual-zone climate control, cruise control, Bluetooth connectivity, nine-speaker sound system with six-CD changer, 18-inch alloy wheels, 10 airbags, HID headlamps, rear parking monitor and automatic windscreen wipers.

SE-I adds: Remote Touch control, electrically operated tailgate, front and rear parking sensors, Lexus Navigation System, 12-spaker audio system, interior wood trim and 19-inch alloy wheels.

SE-L adds: semi-aniline leather upholstery, heated and ventilated front seats, LED headlamps, smart keyless entry and push-button start, 15-speaker Mark Levinson audio with six-DVD changer and DAB module for digital radio reception.

SE-L Premium adds: Lexus's Pre-Crash Safety system and Adaptive Cruise Control, sunroof, Head-Up Display and Active Stabiliser System.