The number of British Islamist fighters rises, and so does the UK's threat level

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Carol Hills: I’m Carol Hills in for Marco Werman and this is The World. Remember the color coded terror alert system that was created post-9/11? We don’t hear about it much these days, at least not here in the US. But over in Britain, they raised their national threat level today to “severe.” Officially, that means a terrorist attack on the United Kingdom is now considered to be highly likely. British authorities won’t talk about specific intelligence about any pending attack but they do say that the higher alert has everything to do with the extremist group known as ISIS. Prime Minister David Cameron says that at least 500 people have traveled from the UK to fight in Syria or Iraq. Prime Minister David Cameron: We need to tackle that ideology of Islamist extremism head on, at root, before it takes the form of violence and terror. That means challenging the thinking of extremist ideologues, identifying the groups in this country that push an extremist agenda and countering them by empowering the overwhelming majority who believe in British values of Democracy, the rule of law and respect for minorities. Hills: We have our BBC colleague Dominic Casciani on the line with us from London, he’s a security analyst. Dominic, how big of a deal is this decision to raise the terror threat? Dominic Casciani: I think, Carol, this is a pretty big deal here in London, particularly for the security officials behind the scenes. But I think for the general public, it’s very, very difficult to compute what’s going on here and really make sense of it. Let me talk you through how it really works. This terror threat level system used to be super-secret in the UK but it was one of the decisions of former Prime Minister Tony Blair’s government to try and be a little more open about this. This was during the days when he was trying to stand shoulder to shoulder with America on all sorts of matters like Afghanistan and Iraq. What the threat level does is give us an idea, an indication, a brief glimpse into the minds of security officials so that when, as today, they say they’re raising it to “severe,” what they’re saying is they’re amassing an awful lot of intelligence from the British security agencies - some of that information may be coming from their partners in Washington - and putting that information together and it’s building a picture of something that’s really concerning them. The picture that’s really concerning them at the moment is Syria and Iraq and the number of British fighters who’ve gone out there to join that Syrian jihad being led by the so-called Islamic State. That’s really what’s going on. Hills: I know there’s been a lot of focus in Britain since the execution video of James Foley and the executioner himself had a British accent. Any indication that increasing the terror alert has to do with evidence or information they found from investigating that person's voice or other Britons who are in Syria? Casciani: The investigation is being kept under a really tight lid at the moment. My understanding is that it’s being led by the security service, MI5, effectively our internal version of the FBI. We understand that there has been significant progress but it’s really speculation to try and work out what that means. What we do know is that there are so many British people that have gone out to Syria; the government estimates about 500 to 600 people who have gone out there, that the security services have a good idea about the lives of some of these people, not least because a lot of them are putting their activities on social media networks, like Twitter. But also at the same time, there’s an awful lot of people who have gone out there who they didn’t have a great deal of an idea about. I was talking to one senior police officer earlier this week who told me that nearly half of those who had left Britain to go to Syria, they haven’t heard of. So if they have identified the man who was involved in this beheading, they’re not saying. I think they’re not saying for very good reason, because they don’t want to compromise the investigation and, in particular, any possible attempt to apprehend people in the field, which would be led by the American authorities. Hills: Prime Minister David Cameron said he’s going to introduce new laws for dealing with terrorism suspects. What’s he talking about? Casciani: This is a real big debate here at the moment in London. For the past two weeks, we’ve had ministers talking about a need for new powers. A couple of years ago, the UK had a very controversial form of house arrest, which was used to keep some terrorism suspects effectively within their own homes for up to 16 hours a day. They weren’t allowed to travel, use mobile phones, use the internet, these kinds of things. That power was watered down a few years ago and is now no longer used. The issue with Syria at the moment has led to many new calls for those powers to be resurrected and for new powers to be created. One of the things the prime minister talked about today was a new and improved power to withhold passports to stop Britons using their British passports to leave the country and to go to Syria. He’s going to announce more details of that next week in parliament. But there’s a real debate about the types of powers the government could use. Hills: BBC security analyst Dominic Casciani in London.