Perhaps in the motor industry as a whole, the jury is still out on the whole question of hybrid cars but the concept has certainly seemed to work for Toyota and its luxury car division Lexus. Since 2000, the company has sold 15,506 Prius hybrids in the UK and a further 6,556 Lexus hybrids, most of them the car that I recently chose for a West Country family holiday, the Lexus RX400h.

When we first tested the car within these pages, we called it a 4x4 with an environmental conscience, two things that may sound contradictory at first glance. Nevertheless, it's difficult to know how else to describe this car. What other petrol-powered luxury 4x4 can you name that averages 35mpg and returns CO2 emissions of under 200g/km? What diesel luxury 4x4 can match these figures come to that?

Of course there are some who feel no guilt about depleting the fossil fuel reserve but even these people's interest could well be piqued by a few of the other fringe benefits of the RX400h. After all, even lazy, selfish people don't want to spend their time queuing in fuel stations. The fuel economy and range of the RX400h means that it'll average around 450 miles on a single fill up. On unfamiliar roads or in freezing weather, that sort of convenience is a real bonus.

Or so I reasoned when choosing this car for the annual family holiday to Dartmouth, a trip of around four hours from where I live in Surrey. Enough of a distance in other words for the kids to get frazzled and the car to guzzle a couple of tankfuls. It helped that my test car was a fully-specced SE-L variant, which meant that it came with DVD screen built into the back of the front headrests. Cue three quiet kids. They even moaned about getting out when we got there, so you can't ask for much more than that.

"A 4x4 with an environmental conscience .."

The RX400h isn't cheap of course, but then you never expected it would be did you? Prices start at £36,415, with plusher SR, SE and SE-L variants offered respectively at £37,500, £40,310 and £45,280. That's a premium of just under £4,500 over a standard petrol-powered RX350. This price difference can be explained to a certain extent by the fact that the RX400h is more powerful than its petrol counterparts, generating a healthy 272bhp. This results in a top speed of 124mph and sprinting capability that can shame some hot hatches. In fact, this heavy 4x4 has jet heels, getting to 60mph in just 7.4 seconds. By contrast, a UK specification RX350 will stop the clock at 7.8 seconds, so you're buying a markedly quicker vehicle, but how does this hybrid technology work?

The 3.3-litre V6 petrol engine under the bonnet isn't anything ground breaking, but Lexus has also engineered a pair of high-torque electric motors positioned front and rear that can either assist the petrol engine during acceleration or replace it altogether at start up or low to mid-range speeds. Moreover, during deceleration and under braking, the engine switches off and both the electric motors act as high-output generators, driven by all four wheels. This regenerative braking system optimises energy management by recovering kinetic energy that would normally be lost as heat as electrical energy for storage in the high performance battery. The battery power level is constantly maintained by the engine-driven generator, which means there is no need for the system to be recharged from an external power source.

The batteries themselves are zero maintenance items guaranteed for 100,000 miles and are a lot more compact than you'd imagine. This sort of drive system is similar to that pioneered in Toyota's Prius but Lexus have finessed certain elements to suit the character of a luxury 4x4. Electrical power enhancements to the new Hybrid Synergy Drive include the use of a boost converter to increase generating capacity. A new, high speed front motor operates at twice the speed and delivers more than double the power of the one used in the Prius. The addition of a rear motor facilitates four-wheel drive and a new high power nickel-metal hydride battery is used. The rearmost motor can deliver a 68bhp boost to the rear wheels when you need maximum acceleration or when the computers detect front wheel slippage. The RX has never been much of a mud plugger but on the twisty little roads around Dartmouth, it proved to be more than adequate.

At all speeds, the Hybrid Synergy Drive system monitors itself for optimum performance and fuel efficiency with minimum emissions and adapts accordingly to run the electric motors in isolation, the engine in isolation, or a combination of both. The driver can see which power sources are being used by means of an instrument readout which replaces the usual rev counter. In versions with satellite navigation, power flow and battery status are shown on a seven-inch colour monitor. This is just as well because when you twist the ignition key, the hybrid mechanism is so quiet that you think nothing is happening.

As for the trip, well Dartmouth and the surrounding villages proved to be as idyllic as ever. We stayed across the River Dart in neighbouring Kingswear and commuted across on the ferry whenever we felt the need. Particularly worth doing is the Riverlink trip (see www.riverlink.co.uk) which enables you to take the steam train from Kingswear to Paignton, board an open-topped bus there, travel to nearby Totnes, then take the ferry that runs from there back to Dartmouth.

An eco-friendly trip made possible by an eco-friendly car. And in a luxury 4x4! Holidays don't get much more satisfying than that..

TOP 5 RX DEALS

The results below show the top RX deals on buyacar

	Lexus RX 400h 3.3 SE 5dr CVT Auto [Multimedia] Off Road
	ETR	Mthly	Saving £4,713	Price £37,932
	Lexus RX 400h 3.3 SR 5dr CVT Auto [Multimedia] Off Road
	ETR	Mthly	Saving £4,456	Price £36,049
	Lexus RX 400h 3.3 SR 5dr CVT Auto Off Road
	ETR	Mthly £636	Saving £4,102	Price £33,453
	Lexus RX 400h 3.3 SR 5dr CVT Auto [Multimedia + ICE] Off Road
	ETR	Mthly	Saving £4,720	Price £37,985
	Lexus RX 400h 3.3 SE-L 5dr CVT Auto Off Road
	ETR	Mthly £770	Saving £4,921	Price £39,454

typical 9.61% APR

PCP finance quote over 48 months,  10,000 miles pa,  deposit of £1000