Is it legal to have the engine running when not in the vehicle?

My Volvo can be started from the phone app - useful for defrosting/warming in the winter and cooling in the summer. (The car remains locked and can't be driven without the key and the driver sitting...

Is it okay to leave a car idling to warm up in the winter?

I have recently changed from a Jaguar F-Pace to an Audi Q8 and am bitterly disappointed with the mobile phone app. The car itself is wonderful but, unlike the Jaguar app, the Audi does not automatically...