Identifying 'radicals' is rather tricky. You're essentially advocating a thought crime.
It's one thing for some loon on the fringes of society to spout nonsense about this, that and the other, but people shouldn't be imprisoned for their views. If that were the case, where do you draw the line? And more importantly, who decides what's 'radical'?
For example, I'm an atheist. I dislike all religions (some more fervently than others) because I believe that they all impose impossible rules and restrictions upon people and then punish them for the 'sin' of being human. I would describe myself has a realist-humanist. However, some might say that I'm a 'radical' atheist. The current Pope almost most certainly would. Radicalism is a term that means many different things to many different people and is therefore extremely subjective.
As for the deportation thing, it's difficult to deport someone who was born in the UK. Where exactly do we deport them to?
However, all that being said, I don't disagree with the sentiment of the original question. I would love to wave a magic wand and have all the violent, oppressive, hate-mongering morons disappear from this country.
But it's just not going to happen as we cannot and should not legislate for 'thought' crimes.