It was certainly done in the past in the UK, usually as a high profile method of enforcing notorious speed sites. I recall the Met carrying a battery powered Vascar system in the back of the old 222's in the early 90's.
Certainly these days it is considered an unsuitable use for a Police Air Ops resource.
Edit - Talking of which I see G-META is still flying !!! Whump Whump Whump
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