SPIRALLING greenhouse gas emission levels have forced major motor manufacturers to take a long hard look at how cars can be more fuel-efficient. casts an eye over some of the latest green contenders.

With a raft of stars from Cameron Diaz to Harrison Ford queuing up to get their hands on one, Toyota’s Prius appears to be setting the benchmark for greener vehicles.

But despite being voted the best European car for 2005 by a panel of top industry figures, like other hybrid motors, this petrol/electric vehicle has yet to make serious inroads in terms of pure sales.

In the first half of 2006 the company shifted just over 2000 cars in the UK – a long way short of seriously contributing to its target of producing a million worldwide by 2010.

Some have put this down to a simple lack of awareness of what hybrid means - a survey by Honda found 40 per cent of drivers were unaware of how these cars function.

Their basic principle revolves around an electric motor which is then recharged by an electric generator that is in turn powered by a fuel-efficient petrol engine that kicks in when extra power is required.

While the take-up appears to have been comparatively slow to date, many in the business are hailing hybrid cars as the way forward.

Tadashi Arashima, president and CEO of Toyota Motor Marketing Europe for one, believed the Prius’s award last year was a major breakthrough.

"We are absolutely delighted to receive the 2005 Car of the Year award . We believe that hybrid technology, in particular as implemented in the Prius with our revolutionary Hybrid Synergy Drive system, represents a big step forward in reducing the environmental impact of automobiles, while at the same time enhancing driving performance."

Though the Prius may not look like the sleekest car on the block and could hardly be tagged as the most affordable, costing between £17,000 and £20,000, it’s not without its boons.

The freshly revamped Mark II models have some smart touches including an easy-to-operate dash-board gearbox and split folding rear seats. It is also surprisingly roomy for a hatchback. Its performance stats of 0-60 in 11 seconds are hardly under par. Naturally, fuel economy lies at its very essence and it is capable of an impressive 56 mpg.

Honda has also recently thrown its hat into the ring with the Hybrid Civic, which rivals the practicality of its conventionally-powered cousins. Like the Prius, it is not going to be winning any beauty contests in a hurry, but then that is hardly its prime aim.

Thankfully the performance figures are not far off from similar-sized saloons, with its 1.4 litre engine managing 0-60 in 12 seconds. It is also competitively priced at £16,250. Both these cars also have the strong selling point of being exempt from congestion charges.

Early indications are that residual figures for these cars will be strong, at least in line with the rest of the Honda range, which will allay concerns of those worried by the new technology.

Though Honda is reported to be aiming to double its European production of hybrid cars to 5,000 a year, this is a modest figure as the vast majority of its sales are in America and Japan.

Toyota’s luxury marque Lexus is in buoyant mood, reporting strong sales of its hybrid models including the 4x4 RX400h at £36,000 and GS450h saloon. The latter boasts eye-brow raising performance from such a comparatively environmentally considerate motor.

Its 3.5 litre V6 engine with electric motor has no trouble in offering a 0-60 time of 5.9 seconds and is priced from £38,000. These two cars now make up a quarter of its overall sales.

Hybrid petrol/electric cars are not the only greener solution – hydrogen powered motors are also starting to spark interest. BMW has just released details of its Hydrogen 7, the first luxury car of its kind which is expected to be available early next year. Based on the existing 7 series, the car can switch easily between petrol and hydrogen power at the touch of a steering-wheel mounted button. When running in hydrogen mode, its only emissions are water vapour.

In theory this sounds great, but the firm are being somewhat tentative about its release with only 100 cars scheduled for production in 2007. Despite this, BMW has long been at the cutting-edge of technological developments, so a mass market unveiling of hydrogen cars is not an unrealistic prospect for the marque.

Keen to keep up, Land Rover has released details of major initiatives to reduce emissions from its production plants and its vehicles. The new Freelander 2 now has 11 per cent reduced emissions on its petrol model and the marque is working on its own hybrid engines.

Another intriguing trend has been the development of Liquefied Petroleum Gas fuelled cars (a mix of propane and butane) which are less harmful to the environment (for more info see www.greenfuel.org.uk/lpg) that may in time be a valuable contributor to emissions reduction targets.

It is apparent the industry’s big players are finally beginning to take action on reducing emissions in a meaningful way. However, the technology is in its infancy and it remains to be seen how long it will take before conventional petrol and diesel engines are surpassed by eco-friendly fuels in the mainstream market.