Encouraged primarily because of its lower CO2 emissions bang for buck. Its why I bought a diesel car. The latest one with a 2016 engine performs rather well in terms of particulates, thanks to the mandatory AdBlu system.

And the massive tax advantages

Ecouraged by tax reductions in the service of CO2 efficiency.

I remember hearing that Mrs Thatcher queried this asking why lean burn petrol wasn't being considered.

Mrs T had a background in chemistry

Petrol emissions are a trade off. Reducing cold start emissions requires a catalytic converter, but they melt if you run too lean. So vehicles actually run richer than required (or efficient) to shrink those first 5 minutes of emissions.

:roll eyes:

Most european car rides are perhaps under 15 minutes, so...