The three city authorities have now been given the power to stop all diesel vehicles that don't comply to the latest Euro 6d TEMP rules from entering. The ruling by the European Court of Justice means vehicles that enter have to emit less than 80mg/km of nitrogen oxides (NOx).
The Euro 6 emissions standard, launched in 2007, originally set an 80mg/km limit according to laboratory tests. Ahead of the WLTP and Real Driving Emissions (RDE) testing procedures introduction in 2017, the EU relaxed the target so that vehicles could emit 168mg/km of NOx, more than double the original limit.
The European court upheld a complaint by the three cities that the relaxed targets allowed "excessively high" local pollution, saying: "the commission did not have the power to amend the Euro 6 emissions limits for the new Real Driving Emissions tests".
It looks likely that Madrid, Paris and Brussels will now push forward a previously proposed ban. It's not clear yet whether other cities will follow suit, but Germany has previously announced that it plans to ban the sale of all petrol and diesel cars by 2030.