There is an implied permission in the UK for people to walk on property, because, after all, you want your letters and newspapers delivered, etc. However, you can specifically cancel that permission, such as the TV licence guys.
Bearing in mind that the "man on the Capham Omnibus" is used as a yardstick in English (not Scottish) law, meaning that judgements are applied according to what a reasonable person would think, I would suggest that landing a helicopter (unless in an emergency) on someone's property would be difficult to justify against walking up the garden path. The same would apply to opening a door having walked up said path.
Phil