It very much depends on your personal situation. Older diesels (around eight years old or more) are already subject to charges when they enter cities such as London, and more cities will take this up in time. However Euro6 diesels and beyond (generally those registered after September 2015) are much cleaner and less polluting.

If you have no intention of entering a city in your older diesel car then that may not be a problem. There are still millions of diesel cars on the road so we don't see them being banned any time soon. If you're concerned about local pollution and you do own a pre-2015 diesel we might consider changing it for a petrol or a newer diesel model.