It’s ugly, slow and Jeremy Clarkson hates it with a passion – but it’s the car that the Government wants you to drive, as motoring editor Peter Carroll explains.

In fact, Gordon Brown loves the Toyota Prius so much it is exempt from today’s announcement of massive car tax hikes.

Why is Mr Brown being so uncharacteristically generous? Because whatever colour the paint job, it’s the greenest car on the road.

Hybrid cars like the Prius used to be a tiny, specialised part of the motor market.

Then came rising oil prices and the credit crunch, and all of a sudden they don’t seem quite such a bad idea after all.

Hard economics mean more of us will be turning to the stable of the Prius.

But just how do these new technology cars work?

The Prius uses a mix of petrol and electric power to replicate the performance of a standard two-litre saloon.

The car has a 1.5-litre petrol engine, but it doesn’t work alone.

Instead, it operates in tandem with a battery-powered electric motor which itself pushes out the equivalent of 67bhp (enough to power a small hatchback).

There’s no need to plug the Prius into an electric socket to keep the batteries topped up as it charges itself while in motion using energy recovered from the petrol engine and the braking process.

The car has a simple automatic transmission so it’s just a case of pressing the starter button, sticking it in Drive, releasing the handbrake and pulling away.

Provided the battery is fully charged it will power the car quietly until speeds of around 30mph are reached.

And, when you get on to open road and accelerate to higher speeds, the petrol engine kicks in – and the extra power is used to charge up the battery ready for when you slow down.

The switch between petrol power and battery power is seamless – the driver simply drives and allows the system to work.

And with its light kerb weight and slippery aerodynamic shape, the car can expect to average a handy 65mpg.

UK drivers, fearful of being stung by huge increases in car tax, have been switching to low emission cars at an unprecedented rate.

The first six months of the year have seen the biggest drop in new car CO2 emissions on record -Êbut it’s rising fuel costs, not environmental concerns, that is largely driving the shift to fuel efficient cars.

A new Toyota Prius costs from £17,900 to £20,800 depending on trim.

Used examples can be had from around £6,000 for an early (2002) model.

Annual savings against traditional petrol cars can be quite considerable. Tax will be nearly £400 cheaper per year compared with a band L gas guzzler and savings of up to 50 per cent could be achieved compared with a car returning 20-25mpg.

However, the latest examples of diesel engines, like the Mini Clubman 1.6D can match the Prius for both emissions and economy.

If you thought typical ‘green’ car owners were weirdy-beardy, tree-hugger types who secretly hate driving and long for cycling to be made compulsory, then think again.

Drivers of these vehicles are likely to be male, urban professionals, on above average incomes who are familiar with the latest technology like electric personal organisers but also have an environmental conscience.

They’re not all new-age blokes however; Esther Rantzen, the doyenne of TV consumer journalism, is already on her second Prius.

“I have run a Prius for several years and I love its economy. It’s clean, quiet and comfortable. And of course it’s green,” says the former star of That’s Life.

Although the car as a whole carries a standard three year warranty Toyota decided to guarantee the hybrid components for eight years or 100,000 miles in order to reassure customers. But not everyone is so enamoured of Toyota’s flagship eco-car, however.

Top Gear’s Jeremy Clarkson hates the Prius and ranks it as one of his ‘least favourite cars in the world.’

“As far as I can see it appeals on no levels at all,” – is his typically blunt verdict.

Nor is it necessarily as economical in real world conditions as you might believe. A pair of journalists drove a Prius together with a BMW 520d from London to Geneva recently and were surprised to find that the Beemer was the more economical.

The hybrid car is here to stay, however – and expect more forms of green technology to become the norm on the road in future years.

Environmental concerns are an issue, yes. But the weakening power of the pound in our pocket is a far stronger draw.

By Peter Carroll