The UK's Special Advisor on Climate change, has stated that the Gov't was wrong to advocate for diesel cars, particularly in Major Cities.
The pollution caused by diesel vehicles has got to a breaking point, and certain Cities will be levying a daily Pollution Tax (Toxin Tax), within the next year.

Several years ago I was in a group(in the Pub) and we were calculating the cost of owning a diesel vehicle compared to petrol.
We found that with increased price of the Diesel engine, and at that time diesel cost more than petrol, it would take approximately 7 years for the average driver to break even, tho' the Diesel engine did get more MPG.

An example ........one Road in South London hit it's Annual Pollution in Five days!

In America/Canada and I think around the World, V/W and Audi were found to be cheating with their diesel pollution levels. When the vehicle was stationary and being tested, it produced much less pollution than when it was being driven. They devised a computer chip to change the levels....am sure people knew about this. V/W has now decided not to sell diesel cars in Canada.

So, better get New Injectors, for the knock..knock car! The Prime Minister stated that the Gov't 'MAY.....get it.....enable a 'buy back'/scrappage program, as it was them that suggested the diesel cars in the first place......