Top ten most economical new cars revealed by the experts who test them in 'real-world' conditions -  with Seat's Leon crowned best

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The Seat Leon and Citroen DS3 are the most economical new cars that have been tested by experts in the last 12 months, according to research from What Car? using its 'true MPG' figures.

Motorists looking for a economical vehicle only have 'official' mile per gallon figures to base their decision on, which are worked out in government tests, then used by manufacturers to promote models.

However, the motoring magazine has its own unique true MPG test which it says shows how the car will truly perform on the road, with many of the official MPG figures being far off the mark.

Seat Leon: The hatchback is the most economical car tested by motoring magazine What Car? in the last year

The true MPG of some models according to What Car? fall well short. The Ford Fiesta Zetec S was furthest away from its EU-sanctioned fuel economy, coming in 37 per cent below claimed consumption figures, with a true MPG of just 39.7 compared to the 62.8 promised.

The next worst offenders were the Alfa Romeo Mito and Volkswagen Polo, with fuel economy 36 per cent lower than promised by the manufacturers. 

In terms of cars which are most economical, the What Car? team - who have tested more than 200 models in the last year - found the top ten were all diesel motors.

Taking the crown for achieving the most miles to the gallon, the Seat Leon 5DR SE Ecomotive 1.6 TDI delivered the best results.

Off the mark: The Ford Fiesta Zetec delivered a 'true' MPG far lower than the official figure

The model, which costs £19,925 brand new, delivered 63.2 MPG, which is still far lower than the 85.6 promised.

Elsewhere, the Citroen DS3 3-HDi Airdream DSport Plus and Mini Cooper D were the two next most efficient vehicles, delivering MPG of 63 and 62.6 respectively, still far lower than official tests claim.

What Car? says it uses cutting-edge test equipment to deliver the true MPG, and tests cars on a variety of real roads, including motorways, A roads, towns and villages.

It has tested 500 models in three years with the average achieving a fuel economy 20 per cent lower than the Government figures.

Jim Holder, What Car? editor, said: 'Buyers get frustrated when they can't achieve claimed fuel economy figures. 

'That's because the official EU tests are carried out in a laboratory under very specific conditions that don't reflect real-world driving.

'However, we took action a few years ago by launching true MPG and have published real-world figures for hundreds of popular vehicles since.'

The figures revealed Vauxhall's VXR8 was the least efficient overall, recording a paltry 19.5MPG. But this was actually a shade higher than the 18.5MPG official data says it delivers.

Least efficient: The What Car? results show the Vauxhall VXR8 is the least efficient car overall

Two other cars in the bottom ten for fuel economy also surpassed their official figures.

The Aston Martin V8 Vantage S has an official MPG of 21.9, whereas What Car? recorded it as 23.2. The Jaguar F-Type R has an official MPG figure of 25.5, compared to the 25.7 the motoring magazine found.

The Citroen C3 VTR+ e-HDi Airdream remains the most efficient car What Car? has tested since 2012 according to true MPG analysis, achieving 70.3MPG.