as somebody who is regually a LHR/LGW spotter and who regually works airside at both security is a bit of a joke. Im a engineer and regually carry a tool case through security with little but x ray examination. I could easily pass a very sharp object to a pax via a drop off point.
Also short of putting a 15ft concrete wall round all airports the permiter fence is easily cut through and a 2 min sprint across the runways in the dark will give you easy acess to many airliners. Not to mention standing somehwre like Richmond or Windsor with a shoulder launched SAM.
There seems to be a great deal of security aimed at pax but this is not the weak point.