I am reading through the Civil Aviation Act (1988) at the moment.
For an Investigator to enter the premises they need;
- Consent.
- Warrant.
For an aircraft;
The investigator may require the person apparently in control of the aircraft, vessel or vehicle to do either or both of the following;
- detain the aircraft, for a reasonable time.
- to ensure that the aircraft is undisturbed.
They can't even make you answer questions without a warrant.
Be careful because if you want to be a smart ass they can get a warrant over the phone pretty easily and I am sure they are always waiting for the next Johnnie Corchran (OJ's Lawyer)