Diesel cars are rubbish town cars. Notwithstanding the debate on particulates etc. they are mechanically rather fragile given all the gubbins that they now have to manage emissions. I have a Vauxhall where the swirl flaps - a half baked invention to try to manage emissions / power at various revs - had decided to come adrift (they get gunged up by that other amazing invention, the EGR) and cause merriment in the engine block. Luckily it was under warranty and a new manifold, turbo and engine rebuild sorted it. But if you think this is only applicable to things like Vauxhalls, BMW have had a very similar problem in the past, with BMW seemingly taking little responsibility when the bits went through the engine. All this is because they are adding in delicate parts at lowest cost and then people are driving their cars such short distances that they get gunged up.
All of this is hotly debated online, with little thought given to the fact that it might be better to simply not drive ridiculously short distances in crowded cities in the first place.