AT the turn of the century, with rising fears about exhaust gases and global warming, the brand new Toyota Prius quickly caught the imagination of badge-wearing environmentalists everywhere, notably Hollywood A-lister Leonardo Di Caprio.

Nearly two decades and more than 3.5 million sales later the first mass-produced hybrid car is still going strong and clean driving technology is moving on apace.

The Prius can rightly claim to have kick-started the whole process and is still at the forefront with deliveries of the latest, fourth-generation model starting in the UK this spring.

The upgrade has brought sharper new looks and enhanced equipment levels to his enduring green machine - and still more improvements in fuel economy and carbon emissions.

The Prius has never been the most exciting car to look at but Toyota's designers have clearly worked hard to give it a more youthful, dynamic feel.

A totally new platform, which will underpin other new Toyotas in the future, has played a major role in that, sitting much lower and giving the car a more road-hugging stance.

Sharper lines and angles elsewhere, bulging wheel arches and some distinctive new light clusters create a more up-to-date effect but may be a little too fussy for some.

A new grade line-up is also introduced emphasising the appeal of the Prius to company car drivers, with new Business Edition and Business Edition Plus versions available. Active trim is the entry level to the range while the Excel version I drove is the flagship.

Interior quality and comfort is improved with the light, airy cabin providing ample head and legroom for five and plenty of storage for their personal items.

Kit levels are also generous across the range with Excel cars benefitting from all the bells and whistles, including premium stereo, seven-inch touchscreen interface, satnav, reversing camera, leather upholstery, heated front seats, a pre-collision braking system and stability and traction control.

But it's the headline efficiency figures which will always be a hybrid's major selling point and new Prius boasts official average fuel consumption of 94.1mpg and carbon emissions of just 70g/km with standard 15-inch wheels.

The 17-inch alloys on my range-topper change those figures to 85.6mpg and 76g/km but that's still hugely impressive and means low running costs and tax.

Driving the new Prius is a much-improved, and surprisingly enjoyable, experience too.

While it will never be sporty, the lower ride height and driving position are satisfying while Toyota's expertise with hybrid technology is now beginning to reap rich rewards.

Pairing a 97bhp, 1.8-litre petrol engine and a 53kW electric motor delivering a further 71bhp with an electric constant variable transmission the system just works really well - offering smooth, relaxed and quiet progress.

The intelligent system aims to operate in electric-only EV mode whenever possible with zero carbon emissions and zero fuel consumption.

This is obviously easier in slower, stop-start urban traffic when less power is required and during my week behind the wheel the clever readout on the dash told me that I was often gliding along without calling upon the engine for more than 40 percent of my daily commute to work.

When a sharp injection of pace is needed, though, the new Prius can deliver. Eco, normal and power drive modes are available and with the latter selected a slight prod on the gas pedal elicits a sharp response from the throttle.

Even in those circumstances, though, the Prius remains very civil, refined and composed - something which I found had a surprisingly calming effect on my driving.

With little or no traditional engine roar everything felt much less hurried and testosterone-fuelled, actually reducing my inclination to mutter obscenities and gesticulate wildly at other drivers over some minor misdemeanor - real or perceived.