I hope he sits in it when it's idling, or is closer than anyone else to it. Otherwise his insurance wouldn't be valid, in the event of it getting stolen. Even if he locks it (with the spare key, for example), all a thief has to do is break a window, and they're away with it.
I believe he's also committing an offence if a car is running, and nobody is in control of it. Though I can't recall which Act, or specific offence it is.
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