Customs and Excise do keep an eye and an ear on what goes on.....
Some years ago I was asked to assist with some details about a flight made by one of our pilots. The pilot had given ATC the correct name of destination, but C&E thought something was suspicious when the a/c set off in what they thought was a totally different direction. All easily explained - the two destinations had similar names. C&E thought the flight was going to an aerodrome in Cheshire, whereas the pilot was actually going to a private site in Cambridgeshire
I'm sure that C&E and the Immigration authorities do keep a discrete eye on light a/c comings and goings, especially in the south-east. A regrettable necessity whilst some low-life still attempt to smuggle drugs and immigrants into the country; when they get caught they deserve no sympathy whatsoever.