While others flutter about discussing a nonevent and Ken rolls out the "K-metrics"--they were certainly missed-- a compelling case for a domestic intelligence agency, er MI5, is made here.
That is, an organization dedicated to "after the fact" (er to catch and prosecute) isn't going to fair well in gathering intelligence, particullarly of the domestic type.
Intelligence gathering, when done well, is a mundane and laborious activity (TV will never run a series on the subject). More importantly, when information is acquired you let it go, freely sharing it with your domestic counterparts (no high profile arrests or TV interviews for these fellows or gals) and immediately get back to the mundane tasks which is your job. If you are successful, we shall never hear of you. If you fail, the beatings will begin which is far less painful then the second guessings. They will make movies about it, factually wrong but adding a little "sex" to the mix, well it was what dreams are made of.