Millions of vehicles on roads in the UK and around the world may be operating without properly certified on-road emissions controls, as a result of test manipulation. Volkswagen Group UK have announced that they are consulting on an action plan to agree ‘technical solutions and measures’, however it is not yet clear whether this will involve a wholesale recall of the offending vehicles or whether this will be at the discretion of the owners. It is also unclear as to whether the post hoc technical solutions will mean that the emission control systems used to pass the tests will be operationalised for real-world use, at the expense of fuel efficiency and CO2 emissions, or whether some alternative solution is possible that can achieve both goals. A simple ‘software tweak’ that removes the ability of vehicle management systems to detect when they are being tested is not sufficient, if those vehicles are then free to continue to generate higher emissions in the real world.