You are cruising along on a sunny day in your gleaming Beamer. Then you hit the inevitable traffic jam. The engine switches off of its own accord. It is saving fuel. Drivers probably won’t feel a kick as the engine purrs into life once more. Investors in carmakers should. It ought to remind them that the industry can, at times, be a tricky play on environmental regulation.

The stop-start tech invented by BMW for these engines is not only smooth. It also helps BMW, along with fellow carmakers, cut costs by adapting to the quirks of an ageing European emissions test. The four decade-old parameters allow cars to stay motionless for 20 per cent of the time. Air conditioning and satnav need not stay on, despite avid use – and fuel costs – in the real world.

It is all a little too like banks. These can cut costs by tweaking capital according to complicated regulations. This works – until someone tweaks the rules. The costs reappear. Now the EU wants to bring its emissions test into the 2010s, potentially in three years.