The fact of the matter is that the reason the BAA wont transfer ID's between airlines is that it makes work for them.
Security is becoming the home for the otherwise un-empolyable that once could only get jobs as heath and safety officers.
Security now has very little to do with keeping the public or the aviation industry safe it's now a gravey train onto which any one who wants to make a quick buck can jump.
The cream of the joke is that no one is allowed to question the great gods of security for fear of being labeled "soft on terrorists".