You ask a big big question bananastand and one you will not get a definitive answer to. Plenty of diverse opinions but no clear cut answers.

My opinion is that EURO 4 cars will be band from town centres, EURO 5 maybe from some and EURO 6 unlikely to be baned.

VAGs fix is causing problems, most are OK with a slight drop in low rev torque but up to 25% of them are having actual faults develop, some are horrendous faults. VAG seam unable to get to the bottom of this and sort the cars out. They are now offering a two year warranty on fuel and emissions system on fixed cars, there are some conditions attached. Other makers are now having to do similar "fixes" so the problems VAG are having could become much more widespread. In the UK there is no requirement to have the fix done.

If I needed the type of car you describe it would be a diesel but I would buy very carefully. I would rather have an unfixed car than a fixed, I would need a long test drive, all day if possible, town, motorway country roads. I would also want to see the condition of the emissions system EGR valve and DPF. Easily done with an OBD device.

HJ is pretty pesamistic about diesel, probably for good reason as he hears of all the horror stories but the fact is the majority run their cars trouble free for very high mileages. Many will disagree with me Im sure.