Drove an Xf2.2D today. 120 miles, roughly 80 on fairly clear motorways although a bit of start and stop for traffic. The rest was on local roads, at least half in traffic. returned over 46MPG. Not a bad car to drive at all and lovely interior, loads of toys and well bolted together.

My SLK 250 CDi (RWD, 201bhp, 500Nm torque) gave me 72.6mpg on my 34 mile commute this morning...

If you want to average over 45mpg without driving like a granny, you should probably be looking at something with an official figure of over 55. That pretty much restricts you to a diesel, but most modern four-pot 2WD diesel cars will manage that (and a few 6-pot ones like the 330d).

It depends what you mean by "economy" and "nice".

This is boring and has been said already, but the cost of petrol is nothing compared to the cost of depreciation. Unless it is kaput, the cheapest car to run is the car you already own because your capital is already sunk into it and you have no doubt endured the worst of the depreciation. A new C-Class is all well and good but the annual depreciation is about £6k a year over three years. That is £500 a month. £1,000 of tax paid income. Of course, you are reminded of the cost of petrol every time you fill up, whereas the depreciation is quietly forgotten about not long after you've depleted your savings of £20,000 or more. If you do less than 12,000miles a year, though, the difference between a 20mpg petrol car and a 50mpg diesel car is only about £185 a month, assuming petrol is £1.40/L and diesel £1.45/L. It is not worth spending £20,000 to obtain this saving.

It has also been noted already that the turbo diesels can be driven economically or they can be driven fast, but not both. Exploit the forced-induction torque in any mid-size 2.0TDI and you'll get about 40mpg. That's what I got out of my BMW 320d. Likewise if you cruise much above the speed limit: fuel consumption increases exponentially with speed. That said, my wife commutes 30miles each way in mixed traffic in a Golf Mk5 2.0TDI and gets 46mpg, although she doesn't drive fast.

But the fact is that any car with a 4-cylinder turbo diesel is never going to be really nice. They are bloody awful engines compared to a six cylinder NA petrol. Even compared to a turbo diesel six they are horrid. They are inherently unrefined and they have very unpleasant power delivery characteristics: nothing, nothing, nothing, WHAM, nothing. Admittedly, modern autos with ten million ratios mask this quite well, but for any enthusiast there is no joy to be found here.

If I had £20,000 for a new used car, I would probably spend £15,000 on a modern petrol six rather than £20,000 on a similar 2.0TDI. I suspect I'd be no worse off financially yet I would have a much nicer car.

And cost yourself ££££££££££££££££s when it goes wrong.

I've spent the last few years smoking round in a Merc SL using the logic described above. However it didn't work out like that - it cost me around 5-6K a year in servicing and repairs (and that's with me doing everything possible).

Sure, there will be a load of people who will pipe up now and say they ran some 16 cylinder German starcruiser for 5 years with nought but an air filter to replace. However there are also people like me who have spent an utter fortune.

Big engine, formerly-expensive cars as a used car proposition almost always ends in tears IME

BMW 320d.

Unless you do a lot of motorway miles I doubt a petrol will come close to 45 mpg. My old Focus 1.8 TDCI does 41 mpg round the doors and a lot more on a run. A newer 320d will easily give you 45 mpg.

Ignore people who only claim to be able to get 30 mpg from diesels. They either don't know how to drive a diesel, drive like a complete nutter or their car is not well. I don't think I could get my old focus under 35 mpg without losing my license.

How long is a few years? 3, 5 maybe? And you're saying you've spent £15,000 - £30,000 in service and repairs???

That would appear to be nuts. Either you've been hugely unlucky or just going about it the wrong way. Curious to know what these costs have actually been for?

My commute is 9 miles. I have to go through 10 roundabouts and 2 sets of traffic lights along single carriage way roads where hold ups are common and traffic is heavy. On cold mornings my car car doesn't even get fully warm till 1 mile before work.

Yet my old 2003 TDCI with 90k on the clock still returns an average of 41 mpg. The worst I have ever seen (calculated properly, not based on the computer)is 39 mpg. On a run it will easily do 50+ mpg.

Like I said, to get 35 mpg I'd have to really be giving it come all the time.

Any newer diesel saloon or hatch should easily be able to get the same or more unless it's a lot bigger or a 4x4.

Also there is some logic to suggest you can't actually get 72mpg while only having covered 34 miles

Got 45mpg out of my Subaru Outback on a longish run the other day. Not bad for 2.5L petrol but I did drive like a granny. And very dull it was too.