The new Toyota Prius is just about the cleverest car on sale on the planet. Its hybrid petrol/electric powertrain is the result of brilliantly clever engineering and it is constructed using a number of cutting-edge technologies.

The Prius makes good old steel-bodied cars using engines which solely burn fuel seem archaic in comparison.

Driving this car should make you feel a little bit condescending to other road users, as you seep out emissions while the rest of the traffic belches along. With 104g/km of carbon dioxide the Prius can certainly claim to be remarkably clean for its size, and with combined economy of 65.7mpg it will sip fuel if you drive it in the right way in the right conditions. Toyota reckons the Prius will expel a tonne less CO2 a year than a very clean diesel car.

Its NOx levels barely register. Toyota claims they are 96% below the Euro IV level of diesel cars. So you can let these impressive figures scroll through your increasingly smug mind as you drive along.

The battery motor is one of the most advanced in a consumer-available car. It is as powerful as many 1.2-litre petrol engines and, Toyota claims, is the most powerful motor for its size and weight in the world. When you pull up at traffic lights, the petrol engine automatically switches off and a gentle getaway will use only electric power.

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Then there's the aerodynamics, which are class- leading, although subjectively speaking the wind-cheating shape has imbued it with all the stylistic elegance of a video remote control. So the list of technology boasts goes on and on, and rightly so.

So why don't I like it? The problem is that despite its intelligence, it falls short on common sense in a number of areas. The powertrain is a staggeringly clever piece of kit and has more than acceptable acceleration, but the whine of the electric motor kicking in – it sounds like a baritone sewing machine – to give the petrol engine some assistance at cruising speeds can get a bit wearing.

On a very laid-back 150-mile round trip up and down the A1, A14 and M11, the car reported it had been running an average of 45.2mpg. You could get this in a diesel without trying, and yet I was consciously driving as efficiently as possible. It would seem that the old Prius' problem of getting nowhere near its claimed combined figure is still not resolved.

Having drive-by-wire brakes is very clever and energy efficient, but the brake feel is poor. Mercedes-Benz has had the same problem with its by-wire braking system.

Building in any feeling of progression instead of something not far from an on-off switch is very difficult.

You would also get the same sort of steering feel if you went down the local arcade and played video games. Combine this non-existent relationship between road and wheel with a jittery ride which seems to make a real fuss of small bumps, and the Prius is not particularly relaxing on a motorway cruise.

I wondered before writing this test whether I should make allowances for shortcomings, but the Prius is a serious piece of kit at £18,000, and should be matched against any other vehicle of its price. Having said that, it's easy to pick faults because Toyota has stuck its head above the parapet with hybrid development, while others have shied away. And you have to applaud the firm for that.

This car is much better to use than its predecessor and will find many homes with green-minded motorists. But measured against the current crop of upper-medium cars in day-to-day use, it falls short.

Delivered price, standard car (P11D value): £18,192 CO2 emissions (g/km): 104
BIK % of P11D in 2004/05: 11%
Graduated VED rate: £65
Insurance group: 8
Combined mpg: 65.7
CAP Monitor residual value: £5,575/31%
Depreciation (20.29 pence per mile x 60,000): £12,174
Maintenance (2.16 pence per mile x 60,000): £1,296
Fuel (5.90 pence per mile x 60,000): £3,540
Wholelife cost (28.35 pence per mile x 60,000): £17,010
Typical contract hire rate: £394 per month