There's 23,000 people on the list of "people of interest". And I've seen calls to "intern them all", in the same way that we interned German citizens in WWII. But there's a few problems with that idea.
The biggest problem is this. How do you get onto that list? One good way is if you say something very inflammatory, and get reported on the hotline. But another good way is if you regularly park outside your neighbour's house, and they get very angry about that, and you get reported on the hotline. In other words, being reported on the hotline gets you put on a list, whether you deserve it or not.
So, first of all, we have Magna Carta. Clause 39, "No free man shall be seized or imprisoned, or stripped of his rights or possessions, or outlawed or exiled, or deprived of his standing in any other way, nor will we proceed with force against him, or send others to do so, except by the lawful judgement of his equals or by the law of the land."
This is an important principle of British justice, and the core of our Constitution (yes, Britain does have a Constitution, it's just that there isn't one single document called "The Constitution"). And without this important safeguard, the state could, without recourse to a court of law, imprison anyone, indefinitely.
You might think "Well, this doesn't apply to me; I'm not a terrorist, or a muslim, or wear a beard". But it does; each time you offend your neighbour (and I've done that in the past), they would have the option of getting you exiled to a prison island by calling the Hotline.
Why was it different in WWII? Well, first of all, it didn't work via denunciation, it was based on someone being a citizen of an enemy country. And secondly, we weren't facing the occasional stabbing, we were facing the Blitz (40,000 killed) and invasion by the Nazi army. And even then, when the Americans interned all the Japanese Americans in WWII, this is now considered to be a very shameful episode (and was considered shameful even at the time, by many).
We did use internment against the IRA. But the threat posed by the IRA was a hundred times as great as that from today's Islamists. Look at the figures.
So ... no. I don't want 23,000 people interned on some prison island just because there might be a few on that list who will take a knife and start stabbing.
And consider this. In 2016, in the UK, there were 32 thousand knife crimes recorded. In London alone, in 2016, 61 people were murdered with knives. And this isn't Islamist Jihad, this is just the background level of knife homicide here. And by the way, gang activity was less than 5% of this.
Yes, of course we need to continue to fight against terror. But while we do that, we should not be terrified into doing something stupid.