Vauxhall Astra

Take Vauxhall's latest Astra. Twenty-five years ago, the hatchback was the size of the current Corsa. It is nearly twice as big now - so surely a 1.3-litre diesel motor wouldn't have the power to shift the practical five-door?

The Luton firm thinks otherwise. It is just dropped its smallest oil-burner into the Astra's roomy engine bay, creating a frugal new entry-level diesel model. Auto Express was first to take the wheel to see whether 1.3 litres is really enough for a modern family car. Already used in the Corsa and Tigra, the unit has been tuned to help cope with the larger Astra's weight. Engineers have squeezed out 89bhp and 200Nm of torque, but on-paper performance is no more than acceptable. The 0-60mph dash takes 12.7 seconds - 1.3 quicker than in the 79bhp 1.7-litre model - and the top speed is 107mph.

Pulling away, the Astra's lack of grunt is obvious. In its relatively narrow powerband it is reasonably brisk, but unless the driver makes fast gearchanges there is a lag in acceleration with every upward shift.

Once up to speed, the six-ratio oil-burner feels less strained and is a refined motorway cruiser. It lacks the more powerful 1.9 CDTI's immediate wave of torque, but drivers who are more interested in mpg than mph will be more than satisfied.

And there is pleasure to be had counting the cost at fuel stations. The Astra returns an impressive 58.9mpg on the combined cycle - 1.1mpg more than the 1.7 CDTI. However, given the lack of power, regular use of full throttle could see the real-life figure drop. Low tax bills are one thing which company car drivers can count on here. The green engine produces only 130g/km of CO2 and is compliant with Euro IV emissions regulations. This allows the Astra to slot easily into the lowest 15 per cent tax bracket.

What's more, in Club trim the 1.3 CDTI is priced ΂£14,895. That's similar to Ford's 89bhp 1.6-litre TDCi Focus, which is only slightly quicker, despite the cost. If your fuel and tax bills are Astra-nomical, get a calculator and work out just how much this Vauxhall could save you. Cars may have become bigger, but that does not mean engines cannot get smaller.