I found what looks to be a reasonable answer in CAP 722 - the UK's drone rules guidance document.
In short, it appears a vessel, vehicle or structure can be under your control if you have the permission of the captain/driver/owner, and any people are under your control. For people to be under your control, they must be willing and able to follow guidance and safety instructions of the pilot.
The long version (correct April 2020):
Article 95(2)(c) makes reference vessels, vehicles and structures being under the control of a remote pilot or operator. A vessel or vehicle could be said to be ‘under the control’ of a person if:
- That vehicle or vessel is present for the purpose of participating in the flight operation; and
- The operator of the vehicle or vessel (for example the driver of a car or captain of a ship) and any passengers are under the control of the remote pilot and can reasonably be expected to follow directions and safety precautions to avoid unplanned interactions with the small unmanned aircraft; and
- The owner or other person with an interest in the vessel or vehicle (such as a lessee) has granted permission for a UAS to operate within 50 metres of that vehicle or vessel.
A structure could be said to be ‘under the control’ of a person if:
- The owner or other person with an interest in the structure (such as a lessee) has granted permission for a UAS to operate within 50 metres of that structure; and
- Any occupants of the structure are under the control of the remote pilot.
For completeness, as the document referes to control of people:
Persons under the control of the SUA operator or remote pilot can generally be defined as:
- Persons solely present for the purpose of participating in the flight operation.
- Persons under the control of the event or site manager who can reasonably be expected to follow directions and safety precautions to avoid unplanned interactions with the small unmanned aircraft. Such persons could include building-site or other industrial workers, film and TV production staff and any other pre-briefed, nominated individuals with an essential task to perform in relation to the event.
Spectators or other persons gathered for sports or other mass public events that have not been specifically established for the purpose of the flying operation are not regarded as being ‘under the control’ of the of the SUA operator or remote pilot.
In principle, persons under the control of the SUA operator or remote pilot at a mass public event must be able to:
- elect to participate or not to participate with the small unmanned aircraft flight operations;
- understand the risk posed to them inherent in the small unmanned aircraft flight operations;
- have reasonable safeguards instituted for them by the site manager and SUA operator during the period of any flight operations;
- not have restrictions placed on their engagement with the purpose of the event or activity for which they are present if they do not elect to participate with the small unmanned aircraft operation.
Note: As an example, it is not sufficient for persons at a public event to have been informed of the operations of the small unmanned aircraft via such means as public address systems, website publishing, e-mail, text and electronic or other means of ticketing, etc. without being also able to satisfy the points above. Permissions have, however, occasionally been granted for small unmanned aircraft flights at public events where these involved a segregated take-off site within the main event, with the aircraft operating only vertically within strict lateral limits that keep it directly overhead the take-off site. Such flights may also be limited by a height restriction and the tolerance of the aircraft to wind effects and battery endurance.