Questionable Legality
What was referred to as "Questionable Legality" in a previous post is, quite simply, a criminal act, and deserves to be treated as such.
In a 'prior incarnation,' as Captain, after an international flight, I always made a thorough inspection of the aircraft, accompanied by our Flight Engineer, because he knew far more about likely hiding places than me. On one flight, we found a large package in an empty bin addressed to someone who was not on board. With my FE as a witness, I took it straight to the Senior Customs Officer. He opened it to find parts of a copy (but lethal) M16 Rifle. He called the Police and had the addressee investigated, charged and thrown into clink.
Although not quite so dramatic, BA Captains should, in the present circumstances, take similar precautions and have any miscreants face the full process of the law.