LH2-security staff DO have a legal right to search you
Wrong wrong wrong. It is a condition of entry, not a legal right. If you discover you have left a large hunting knife in your bag, they can't demand to search your person and your bag if you decide not to proceed through security.
It's an IMPORTANT distinction. They can inform the Police but they are warranted officers of the law. Security staff are not permitted to frog march you anywhere, that's a Police matter again. Forcibly doing so without a compelling reason to manhandle someone is assault.
Geez life used to be simpler than this ...