While there are exceptions, I have to say that most of the individual security agents I deal with are polite and friendly if you are polite and friendly with them. The problem with UK airport security lies higher up the chain of command than the individual gate agent.
Under our devolved system airport security managers can add additional local rules above that required by the regulator, so that at some airports a non locally based member of staff cannot access the ramp without local pass holding escort, at others they can; at some airports all belts must be removed whether or not they trigger the scanner, at others you are fine, and the scanners themselves seem set to different sensitivities - my metal bracelet watch triggers some but not others.
The devolved system is of course a convenient cop out by the regulator, allowing them to saddle the blame for any problem onto the airports manager - "we gave you the power to put additional local rules in place so its your fault", and naturally the local security manager does just that to cover their ass, leading to the inconsistent system we suffer. The purpose of a regulator is to provide consistent proportionate regulation, not to farm out regulation to allow it to shirk its responsibilities.
Our employers the airlines also appear remiss in supinely accepting this: I recently changed base; despite my pass at my previous airport have significant validity left we had to got through the whole rigmarole or CRC and security and CRC checks to get a new on issued - inconvenient for me and a additional cost for my airline at a time we have seen a number of airline in financial trouble. Why each airport has to start the whole process from scratch when somebody already holds a valid uk airport security pass I find inexplicable.
There are also safety implications: On the continent a number of airports use a sensible system of coded numeric keypads to allow access from the airbridge to the ramp and vice versa. In the Uk I typically cannot get that access to deal with say fuelers, or issues in the hold etc, unless I am at my home airport for which I hold a pass. More importantly if when on the ramp I need quick access to my aircraft - of which I am the captain, and for which I am responsible - I may not be able to quickly get it.
Finally I note our union BALPA seems almost deafening in it silence, its latest missives seem to be representing the edicts of the security authorities to the pilots, rather than the concerns and needs of the pilots to the authorities. Why for example when on duty but positioning as a passenger, do I suddenly become a more dangerous person, denied access to my crewroom to get the flight documentation that I will use later to conduct a flight, until the end of the positioning flight when my status magically changes back to that of operating crew, and I am allowed into the places I need to go to do my job?