OK, as you have spent the time, I'll try to answer each an every point you have made.
Archways can be set to be less or more sensitive...
You made the point well. If I ping either the threshold or the random selector I get extra treatment. So be it, that's life.
I hope you'd agree that it's only logical to have a standard procedure for any alarm...
You are correct and I totally agree. But I dislike the attitude that typically goes along with the procedure.
I do agree that there can be some small variance in interpretation.
I disagree, it's a huge variation.
DfT guidance to airports, not a regulation
Probably the real culprits.
"...sadly all the remainder (probably 15 cases) were caused by rude and aggressive crew..."
Unfortunately, I think you are correct. Too many crew try to take on security at the checkpoint. A pointless and futile proposition.
Lastly, I'm not UK crew. Our security department despairs at UK security. They believe it is just a cost of doing business in the UK. And I have tried to speak with the powers that be. I left with no doubt about what they thought of me.