If particulates are the problem, which seems to be the issue here, surely they can be filtered out of emissions. A filter on diesel exhausts and a means to dispose of the particulates safely can't be too much to ask, compared with a total ban.
My view is they tax the majority. Diesel started becoming popular because it had less tax on it. Once diesel vehicles got on a 50/50 par with petrol, they equalized the tax. Then diesel outstripped petrol vehicles, the tax was loaded onto diesel, more than petrol.
It's about revenue, the environment issues just give them an excuse.
I should add IMO, and not based on any published data.