Brian Gaff wrote:

Did they not develop a particulate filter some years ago, for this problem,
or is the issue that its very costly to make and needs to be cleaned out too
often.

They did and any diesel car under about 7 years old will have one, they
are not ideal for cars that only do short journeys as they don't get the
opportunity to "burn off" the ash they collect, they certainly do stop
the visible blue/grey clouds out the exhaust. I'm not sure what the
smallest particles the DPFs collect is, PM10 seems to be the size
complained about, and they won't stop the NOx.