Building on lessons learnt by Toyota, maker of the Prius, Lexus launched the RX 400h in 2005 for 4x4 drivers who wanted the safety and convenience of an off-roader but didn’t want to offend their green neighbours. With it, 4x4 drivers could glide through the city using only electric motors for emissions-free motoring at speeds up to 20mph.

The world’s first 4x4 hybrid, its secret lies beneath the rear seats, where an array of batteries holds power for two electric motors — one each for the front and rear axles. Under the bonnet, where you’d typically expect a large V8 engine, is instead a 3311cc V6.

Lexus, Toyota’s luxury subsidiary, claims this petrol-electric combination results in a car with the performance of a 4 litre petrol one (hence the 400 designation), but fuel economy on a par with a diesel SUV. Indeed official data reveal 269bhp, a 0-60mph time of 7.6sec, fuel economy of 34.9mpg in the combined cycle, and CO2 emissions of 192g/km.

Lexus sold 9,021 of these hybrids in the UK up to May 2008 — a respectable number. The concept of a high-performance SUV with palatable fuel economy and quite low exhaust emissions and company car taxes clearly struck a chord.

Finding a good used one is not that difficult. Prices start at about £22,000 for the earliest examples — a premium of some £6,500 (over the conventional RX 300) for the hybrid technology. With Lexus’s excellent reliability, you needn’t worry about being let down. Batteries are apparently good for the life of the new-car warranty, and owners say that even beyond this, high-mileage examples are running trouble-free.

Externally, nothing apart from a badge differentiates the hybrid RX from the RX 300. Inside, it’s much the same — comfortable seats, a generous specification and superb optional sat nav. Only the replacement of the rev counter with an electric power meter hints at what lies beneath.

Turn the key, and there’s no engine roar, just a solitary warning beep to tell you all systems are go. At low speeds the batteries do the work and the silence remains. It’s only as speed gathers to 20mph, or a sudden surge of power is demanded, that the V6 engine joins in, working with the continuously variable transmission (CVT) to add power and potentially take the Lexus up to its 124mph maximum.

Driven with vigour, the RX 400h has big performance but offers no economy benefit. But ease off the throttle and let the batteries take the strain and the potential of hybrid technology becomes apparent. The Lexus can better 30mpg, and at low speeds is eerily silent.

The CVT seamlessly combines both power sources, as does the four-wheel drive, which sees petrol and electric power directed to the front wheels — unless a loss of traction is detected, in which case the second electric motor sends power to the rear axle. It is all extraordinarily effective.

If you want an SUV that’s greener than the rest, at a price that won’t cause a short circuit, the Lexus RX 400h really is a worthwhile option.

CHECK THE FOLLOWING:

BATTERIES Stored under rear seat and don’t steal space
BOOT SPACE Not huge atstandard on the SE-L model
GEARBOX Look for seamless operation in use
HEADLIGHTS SE and SE-L versions have adaptive front lighting — headlamps turn for improved vision through bends
SAFETY No Euro NCAP score, but nine airbags suggest good protection
SAT NAV Superb touchscreen system standard on SE-L version
TAILGATE Some have sticky latches, so check this
TOWING CAPACITY Limited to 2,000kg, so not great

VITAL STATISTICS

MODEL Lexus RX 400h 3.3 SE-L hybrid
ENGINE3311cc, six cylinders
ELECTRIC MOTORS Two
COMBINED POWER269bhp
TRANSMISSION CVT automatic
FUEL/CO234.9mpg (combined)/192g/km
ACCELERATION0-62mph: 7.6 sec
TOP SPEED124mph
COST NEW (2006)£43,565
ROAD TAX BAND F (£210 for 12 months)

VALUES

MILEAGE 10,000 20,000 40,000
2005 (05) Trade £23,250 £21,850 £19,250 Retail £26,000 £24,750 £ 22,000
2006 (06) Trade £26,250 £24,650 £21,800 Retail £29,250 £27,750 £25,000
2007 (07) Trade £29,800 £28,000 £24,750 Retail £32,750 £31,000 £27,750

THE ONE TO BUY
A 2006 06 Lexus RX 400h SE-L with 20,000 miles on the clock. Pay £27,750 at a dealer, or £26,500 privately

OR FOR SIMILAR MONEY
2006 56 Mercedes-Benz ML 320 CDI SE
2007 56 Land Rover Discovery 2.7TD V6 HSE
2007 56 Volvo XC90 2.4 D5 SE Lux
2007 07 VW Touareg 3.0 V6 TDI Altitude 2007 07 Toyota Land Cruiser 3.0 D-4D