I'LL never forget my astonishment a few years ago when I was cruising at between 60 and 70 miles an hour on a quiet dual carriageway.

I glanced at the trip computer of the Audi A6 diesel I was driving - which was set on economy - and it was showing an average of 60 miles per gallon.

Now the A6 is not a small light car, it's a big hefty one, so I was amazed how frugal it could be.

The last A6 was produced from 2011 to 2018 and despite holding its value better than most, it's much more affordable a few years down the line.

And like other well-built executive cars, as long as full service history is part of the deal, older cars with high mileage can be an absolute bargain and still not cause any problems.

All Audi's products are very well built and of course, even the more ordinary of them drive beautifully.

That said, this model doesn't match up to its main opposition - the BMW 5 Series and Jaguar XF - when it comes to driving enjoyment.

A good saloon or Avant estate could still be just what you are looking for but drive it for a few miles to make sure you like it.

The A6 has a very wide array of different engine options - the majority with an automatic gearbox, but since 2011, petrols have ranged from a 1.8 turbo with 187bhp, through a 2.0-litre with 248 to a 3 litre with 305 and a 4.0-litre V8 with 443 in the very sporting S6.

With these kind of power outputs, performance is very good to superb - as you can imagine. Even the 1.8 accelerates from zero to 60 miles an hour in 7.6 seconds, and the S6 takes just 4.3, putting it right up there in the supercar league.

But the 1.8 at least is still capable of 49mpg and comes with decently low emissions.

Diesels are 2.0 and 3.0-litres and have power ranging up from an excellent 174bhp to a heady 305 in the BiTurbo.

These make up the majority of cars on the secondhand market, because most were originally bought or leased as company cars.

Again, performance is excellent, with 0-60 for the 2.0-litre at 7.5 seconds, and economy of 56mpg. Emissions are lower than the petrols of course and for this same model, CO2 is just 114 grammes per kilometre.

The top 3.0-litre BiTurbo sprints to 60 in a very quick 4.8 seconds. Yet it is still rated at 47 miles per gallon.

Handling and roadholding are marvellous, with tenacious grip and very good balance through the corners.

This excellence is let down by steering that's a little lacking in feel, but this is something that owners soon get used to.

Refinement is superb at any speed but personally, I would avoid any with sports suspension. The standard setup takes the cars round the corners just as well, and gives a noticeably more comfortable ride.

Likewise, and for the same reason, avoid the larger wheels and tyres.

Of course, Audi's excellent quattro four wheel drive system is available on most models and standard on some, and this improves the already excellent roadholding, as well as giving the security of top level traction in snow and ice.

The quality of fit and finish inside and out is superb, and should still be good even years down the line.

All have hard-feeling but comfortable seats, and a high level of equipment including traction control, auto headlights and wipers, climate and a multi-function steering wheel.

They also have Audi's adjustable Dynamic Suspension, Drive select, which allows the driver to choose between different levels of accelerator response, cruise control, a parking system with front and rear sensors and leather upholstery.

Also standard are Bluetooth, non-touch screen sat nav and voice activation for many functions.

Pay about £10,600 for a '15 15-reg 2.0 TDI SE auto, or £19,900 for an '18 18-reg 1.8 TFSI S-line auto.