I know of one case where the pilot of a twin engined helicopter (not me) was reported to the CAA by LHR ATC. In that case it was for alleged contravention of the low flying regulations (pilot descended to maintain VMC).
As a chief pilot I was once asked to respond to a threatening letter from the CAA legal branch (which, from its tone, appeared to be have been composed by an office junior) regarding an allegation of continued breaches of the 500 ft rule during take off and landing, causing unnecessary noise and danger.
My reply was that although we always tried to minimise noise nuisance and flew to Class A profiles, the 500 ft rule didn’t actually apply to our aircraft when taking off or landing at our (registered and CAA approved) helipad and that in any case, as a police air support unit, we were exempt the low flying rules as per our CAA approved operations manual.
Never heard anything further.