This is a academic question. In real life you will find each night hundreds of helicopters in the PPRuNe world unattented. Or what do you think? The business is allways near the customer, out in the green. The pilot is often alone. Fences and guards around their ships have only the plank drivers. And every night a security guard?
Forget it.
I leaved helicopters unattended across europe, but not in UK
and the best situation i found was the day some teens having a big party in front of a real helicopter, with campfire, kissing and so on. Very friendly outcome allways. But a bad feeling stays.