MUCH has been said about hybrid cars yet exactly what goes on under the bonnet remains a mystery for many a driver.

Toyota has just shed a little light on the matter by fitting its new Yaris hybrid with some clever telemetry to demonstrate how the petrol-electric powertrain performs in everyday conditions.

The results are an eye-opener and show just what a modern hybrid can do to keep emissions low and save money at the pumps.

The new Yaris - now priced from £15,995 - is still the cheapest full hybrid on sale in the UK and with a 1.5-litre petrol engine hooked up to an electric motor it produces 98bhp.

On paper that gives it a 0 to 60 acceleration time of 11.8 seconds, a maximum of 103mph yet has a CO2 figure as low as 75g/km equating to 85.6mpg.

Under the new car tax system that will cost private buyers £25 in the first year and £140 a year thereafter and presents business users with a 13 per cent benefit in kind banding.

The hybrid is available in all six Yaris trim levels and the range topping Excel models we tried cost from £19,295 - £1,800 more than the conventionally-powered and equally new 1.5-litre manual version.

In Excel trim the Yaris sits on 16-inch alloys and the larger wheel size has a significant impact on economy, reducing the overall fuel figure to 78.5mpg with emissions of 82g/km.

Fitted with a Driveco monitoring device to capture data over every inch of the journey the Yaris hybrid covered some 40 miles, showing an average of 60mpg on the trip computer at the end of the drive.

Analysing the data revealed the car had managed to complete a third of the route on electric power alone and had spent more than half of the journey time in EV mode.

Admittedly, the exercise was carried out in Holland where roads are not that challenging but traffic conditions are demanding and speed limits are frequently less than 20mph.

In fact, our 40 mile drive through the bulb fields and villages around Amsterdam took the best part of two hours, comparable to a rush hour commute.

Repeating the route in a 1.5-litre non-hybrid Yaris - official consumption on 16-inch wheels 56.5mpg with a CO2 rating of 112g/km - saw an average of 50 to the gallon, still impressive given the conditions but crucially nowhere near as environmentally friendly as the hybrid.

While the better economy of the hybrid will result in fuel cost savings of around £150 over 10,000 miles, it is on the emissions front where the difference is greatest.

On our drives the Yaris hybrid produced 6.21kg of CO2 while the conventional model pumped out more than eight kilos. That works out at a saving of around half a tonne of CO2 a year - the equivalent of flying from London to North Africa.

Toyota has also made some changes to improve refinement on the Yaris hybrid and these include alterations to the subframe and the exhaust system to reduce booming inside the car.

There are also tweaks to the steering, the shock absorbers and the engine mounts and all in all the hybrid is much quieter and comfortable than before, and that includes the CVT automatic transmission.

As with all new versions of the Yaris there's a new-look to the nose with a wider grille, redesigned head lights, changes to the side panels and the tailgate where the rear light clusters now extend across.

The line up - still built at Toyota's French factory - no longer includes three door models and as well as replacing the 1.33-litre model with the new 1.5-litre 110bhp engine, diesels have also been dropped from the range.

Inside, the touchscreen is now integrated into the dash and there instrument panel now incorporates a TFT display between the dials.

The three-cylinder Yaris 1.0-litre remains the entry-level model priced from £12,495 while the new 1.5-litre version is priced from £15,295.

A new high grade Bi-Tone trim level is also being introduced with different coloured roofs to boost the Yaris' appeal to younger buyers and those versions are priced from £17,595.

The Driveco telemetry system is for demonstration purposes only and is being rolled out be Toyota across Europe for retailers to show potential customers how hybrid models perform in real world conditions.