Howard, I see political incompetence as follows.
The consumer was pushed into diesel ownership on a massive scale. We're now being told that this was a bad move. The science was available and the government didn't exercise due diligence. That's incompetent. Hell, even Top Gear highlighted the poor air quality in London was directly related to Diesel vehicles and that was years ago.
Despite this, used diesel cars, which are now considered undesirable, retain their tax breaks. That's incompetence.
The criteria for measuring and categorising motor vehicles have long been known to be almost without merit. The figures which are used to tax or even ban certain vehicles are known to be wildly inaccurate and yet they've remained in place for years. That's incompetent.
The government hasn't addressed, or even clarified, how diesel cars are to be treated in the short and long terms. That's directly responsible for the uncertainty in the market and the major slump in sales. That's incompetent.
Manufacturers are allowed to claim environmental benefits using "scrappage" schemes. There is no legislation that I know of,that requires these claims to be verified. I would doubt very much if there's any overall environmental benefit in scrapping a perfectly good five year old car and building a new one.
Unfortunately the great British public seem increasingly keen to jump on whichever bandwagon rolls past.