I often visit PMI with a pass provided by AENA.
First of all the questions asked at U.K. airports: Did you pack your own case Yes/No..........what are you going to say. Are you carrying anything for anyone etc. etc. Nobody wires you up to a lie detector!
I can assure you, you will not get out of the gates without the necessary credentials. All gates are swipe card controlled.
CCTV coverage also appears efficient as I am regularly stopped by their contracted security or La Guardia Civil in the airside, even with a pass around my neck and high - vis.. I don't suggest you try it!
Last time I was stopped by four La G.C. and even though I was meant to be there, it sure raises the hair on the back of your neck.
Buenos tardes.