<p style=”text-align: left;”>WardyGTC what you describe is a bit different. Leaving your car running while the driver gets out is the offence of “Quitting” which is based on a running car should never be left alone in case something goes wrong.</p>
Unnecessary idling is any idling of a vehicle on a public road when it isnt in a flow of traffic such as stopped at lights or in traffic etc.
Your not allowed to stand with your engine running while parked and isnt a new thing.
The key point is “public road” as you can do what you like in a shop car park etc as that’s private property.