It takes some getting used to that a car the size of the Lexus RX, with performance that sees it break 8 seconds for the 0-62mph run with ease, can nevertheless produce nearly 35mph on the combined cycle and cough out less than 200g/km of CO2. In the very early 21st century, this series of statistics just doesn't compute for any production vehicle using a conventional petrol or diesel engine.And of course the whole point about the 400h is that it isn't conventional at all. Toyota - whether building cars under its own name or the Lexus brand - is very keen on introducing hybrid techology, and that's what makes this SUV perform such tricks. A 3.3-litre V6 engine produces most of the power, but depending on circumstances it is either enhanced or replaced by two electric motors, one operating on each of the front and rear axles.Unlike in, for example, the Toyota Prius, there is very little dashboard information to alert you to the various changes - just one large dial telling you whether the battery pack is giving or receiving power. You don't really hear what's going on, either. In most circumstances the 400h will drift away from a standstill with the engine switched off, and that engine is so quiet that you are barely aware of the moment when it comes into play. It's something you feel more than see.From the outside, of course, the 400h is very quiet, too, and as with all hybrids I'm slightly concerned about the way it moves from rest in almost complete silence. It's advisable to make sure that no pedestrians are likely to stray into your path as you ease away from traffic lights.On the other hand, if you floor the throttle there's a rather decent roar from that V6 engine. On its own, it produces just over 200bhp, but that's enhanced to just under 270bhp with the help of the electric motors. The resulting acceleration is quite stirring, and it still requires the use of a surprisingly small amount of fuel since the motors' power was all gained through regenerative braking.Even though it's heavier than the recently-introduced RX 350 (see launch report), it performs in much the same way, with a 0-62mph time 0.2 seconds better than the non-hybrid. At the same time, it blows that car out of the water in terms of fuel economy and CO2 emissions.There is actually more performance than I feel the rest of the car can deal with. Epoch-making though it may be in other respects, the RX does not feel particularly advanced on the road. There is more front-end bounce than seems absolutely necessary, and in damp conditions understeer starts to chime in a bit earlier than I would expect even of a large, heavy SUV.This in spite of the Lexus Vehicle Dynamics Integrated Management system, which combines the functions of the ABS, EBD, hybrid drive, traction control, vehicle stability control and four-wheel drive operations. I'm sure that VDIM will get you out of trouble in an emergency, but as is often the way with these things I'd be happier if the plain old mechanical suspension had been set up in a more confidence-inspiring manner.It's comfortable enough to drive, all the same, and there's room for five sturdy adults. You can also pile a lot stuff in the boot, even though the floor is inevitably quite high, and if you need to adjust the bias towards inanimate cargo you can slide the rear seats forward. Even in their rearmost position, though, they still leave a gap in front of the load cover, so try as you might you can't entirely keep everything out of sight.Prices for the 400h start at £35,480, but the car tested here is in SE-L specification, which costs £44,345. For that you get, among other items, a Bluetooth interface, an 11-speaker Mark Levinson sound system, a real-time video showing you what's behind the car when you reverse, a CD text function and the Lexus Navigator satnav system with traffic avoidance and voice recognition, all of which are either optional or not available at all on lesser models.I won't trouble you with the price adjustment table which Lexus has made available to the media. The basic point of it is that the company claims the 400h is better value for money than its major competitors on specification alone. It's certainly hard to think of anyone else who offers so much for the price - and that's even before you consider all the hybrid trickery which, at the time of writing, nobody else in the sector supplies.For all that, the 400h is not the most interesting SUV to live with, or at least not once you've stopped giggling at the way it will move away from a standstill with the engine switched off. Comparing what you pay with what you get makes it look more attractive, though, and the economy/emissions issue - if it's something that buyers of large SUVs actually worry about to any extent - could well be enough to put it at the top of the list. Engine 3311cc, 6 cylinders Power 269bhp Fuel/CO2 34.9mpg / 192g/km Acceleration 0-62mph: 7.6 seconds Top speed 124mph Price £44,345 Details correct at publication date