Looks likely to be one of the National Grid AS355's doing powerline surveys or lifting during repairs.
If you look a ~100 metres to the W you will see high tension power lines.
The scheme is unsubtle & fairly obvious...
http://www.!!!!!!!!!!!!!!/open.file/0327433/M/
http://www.!!!!!!!!!!!!!!/open.file/1017372/M/
http://www.!!!!!!!!!!!!!!/open.file/0606407/M/