I’ve just driven the new Subaru Legacy diesel and to say I’m deeply impressed would be a major understatement.  

The flat-four diesel motor doesn’t just transform the Legacy, it gives the whole brand a new impetus in the UK. It’s not an exaggeration to say that the new engine – and its inevitable spread throughout the model range – is likely to save Subaru from the sales annihilation its petrol models’ profligate CO2 outputs threatened to trigger.

I’d be very surprised if a substantial majority of British-bought Scoobies weren’t packing the new motor in a year’s time: it really is that good.

Most impressive is the way it delivers on economy – long the bane of modern turbo-diesels, which tend to fall considerably short of the grandiose claims made for them in real world use.

Several years ago I ran a previous-gen Legacy 2.0-litre petrol which managed to combine utter gutlessness with fuel consumption to rival a recently torpedoed supertanker – I think the best it ever managed on a gentle run was 25mpg, and enthusiastic use would push it down to the mid-teens.

The new diesel version is empirically quicker – 8.5 seconds for the 0-62 dash is hardly hanging around in anyone’s book – but it’s also remarkably frugal. Taking a gentle run at my 130 mile commute home and back, including urban sprawl, motorways and ‘A’ roads, saw an average of 50.7mpg according to the trip computer.

For a 1510kg estate car fitted with proper, permanent four-wheel drive system, that’s not just good – it’s unprecedented.