Interesting question. Not sure if I have answered it. Some thoughts.
If I was the AMHP, and I believed that P could be carrying, and thus poses a risk to others, whether that be the ‘assessors’, or those tasked with conveying P to the hospital then I would be asking for the assistance of the Police from the very beginning. Police intelligence, previous convictions, MAPPA Category 2, documented risk in HCR-20, etc, means there is an onus on the AMHP to consider the safety of all those involved. in the assessment and conveyance.
Ambulance Service, as well as Sec 12 Doctor etc would all be notified of the risk. Their employers have a duty to make sure that their employees are protected from harm. All of this would be considered in the planning phase. If I was not satisfied that there were sufficient measures in place, I would not proceed with the assessment and I know my Manager would be on board with this. This is the perfect scenario. Time to discuss, plan and document.
Of course, there could be occasions when this information emerges at any point in the assessment or conveyance. For example, Ambulance crew see something that looks like a concealed weapon. If P is asked if this is the case, and P denies, but suspicion remains, then I do not think that the obligation to convey would out weigh the safety of the crew and potentially P. Then no convey. Notify Police, and they can consider PACE. I recall Police using PACE, as long as they have reasonable grounds that they are acting to save life and limb, they are covered. This I believe applies to someone’s home and outside of the home
I don’t think that the MHA at the point of conveyance would provide the legal authority to search P. I believe searches of inpatients are done under ‘common law’, though its possible there is a difference between P who is a 131 patient, or a transferred prisoner. I guess you could make a case that security of staff and fellow patients is covered by the MHA, though it is not explicit, more implied. Inpatient staff have the physical and procedural security that would allow searches to be done in a safe way.
Yes you could make a case that you could search under common law at the point of conveying, but consent would need to be obtained. I think as soon as P says no, and would resist such a search, you are then having to consider restraints. Undertaking a search and using restraints to do this, is not going to be covered by any operational policy. You are going to be left vulnerable to all kinds of problems, not only from your employer, but possibly the Courts and your registering body.
Now I am going to contradict the above, and include an emergency scenario. You believe that the P is going to harm self or others, been told they have a knife on person, appearing to reach for it, no time to call Police, cannot extract yourself from the situation, trapped in a corner, restrain P and remove item. You could then rely upon necessity/common law.