Diesel engines in cars are not the problem, nor are the engines in commercial vehicles. These are the cleanest they have ever been now at Euro6, bugger all comes out of them.
The problem is the government analysing old data. Typically they are looking at older models all the time, even 2 years ago, this is an old model.

The cheapest fix is to apply the changes to road transport. Maybe they should ban ship engines, or maybe look at aviation fuel, the amount these colossal vehicles burn is xxx times more than road transport. Just easier to apply the cost to change to the wheeled variety.