I sincerely doubt you can detect "radicalization" by keyword matching. The process of becoming familiar with any philosophy/ideology/religion is quite a bit more subtle than a search for keywords. I bet you could get "radicalized" and never actually use any of the keywords mentioned. For instance, I've heard people say that they became atheists while sitting in a church listening to a sermon. As I recall, the story had to do with the usual "lake of fire" reserved for sinners, and what trivial sins would condemn one to eternity in that lake of fire. Reasoning from first principles, the story-teller became an atheist.
So, this software won't do it's stated purpose, because it can't. That means that the software will experience "mission creep". What's the likely end point of that? Real-time monitoring of all children's internet access in the UK? Does that seems like a good idea to anyone other than a creepy spook/"cleared" person?