That wouldn't make any sense. Governments set the tests. Government officials invigilate them. It would mean Governments stating "sorry, we have misled everyone and it's going to cost you all a fortune." They aren't going to do that. MoT tests were changing in 2017 anyway. And from April 2017 annual tax on all new cars will be £140pa regardless of CO2 emissions, plus a £310pa luxury tax for cars over £40,000. So the emphasis was shifting from CO2 tax anyway to favour higher CO2 but lower NOx petrol engines.