(CNN) -- Armed police shut down a busy motorway in central England Thursday amid a security alert centred on a bus, a stark reminder of the heightened watch being maintained by authorities just three weeks before the London Olympic Games.
Hours earlier, police in London arrested six people on terror charges but said the operation was unrelated to the Olympics, which begin in late July.
While police concluded that the incident on the bus presented no threat, terror-related or otherwise, security is a central concern for UK authorities and Olympic organizers ahead of the games.
CNN Senior International Correspondent Nic Robertson explains what's behind Thursday's police operations.
What does the police response to the bus incident mean?
What this tells us is that while this incident was completely unrelated to the Olympics, the counter-terrorism authorities and police are ready on a hair-trigger to respond in an incredibly fast, positive and organized way to any perceived security threats.
Thursday's events are symptomatic of the police preparing and raising their level of concern about people who may be plotting events related to the Olympics. We saw the police in London arrest six people on Thursday -- although they say it's not related to the Olympics, they say it's related to credible threats against sites in the United Kingdom.
What we are seeing in the lead-up to the Olympics is the police and intelligence authorities taking absolutely no chances.
Security during the Olympics will be at an all-time high. Has that operation already begun?
Olympic security has already begun. The police, the army and the hazardous materials people were ready on a hair-trigger, and they will already be analyzing how quickly the response times were for today's incident. And they will have units around London that are ready to move that quickly.
When you see the arrests Thursday, the arrests last week and even the arrest of two men from ETA (Basque separatist group) last week in London, it gives the impression that anything going on out there, any group the police are aware of... they're taking no chances and they're just wrapping everyone up.
What can people expect when they come to London for the Olympics?
I think you can expect to be thoroughly searched entering the Olympic site. You can expect to see a much greater security presence on the streets -- we were already told by one person who advises the government on defense and terrorism issues that the increased helicopter activity we're seeing now in London is just so people get used to the fact there are going to be more military helicopters flying around during the Olympics, and I think we're going to see more of that type of activity.
We're already seeing more police in uniform around the city. Witness the arrests, and the things we're aware the police have been doing the past couple of weeks, and it's clear the Olympic level security is already underway.
Is there a risk of civil liberties being infringed?
It's safe to say that at times like this you can assume that the police and intelligence authorities won't be taking any chances. There may be civil liberties advocates who will complain in hindsight -- but the British government has said recently that it has an obligation to provide security during the Olympics. At the end of the day, if you're a police officer you can't afford to take any risks.
What other options are police considering to prevent attacks?
The police are looking at people who have been in jail on terrorist convictions who are still considered a danger and are out on license [probation] -- they're looking at ways to make sure they can not pose a threat, make sure they is no reason to put them back in jail for example.
In the past 18 months, between 50 and 80 terror convicts have been released from prison, and many of them are in east London, where the bulk of the Olympics will be held. So the police are considering what they can do with the people who've been released on license who they consider dangerous.
One thing they're considering is finding ways to make sure these people are not on the streets of London for the period of the Olympics. That's not something the police are making public, and it's not something that has necessarily happened, it's just something that's under serious consideration, which gives you an idea of how sensitive the police are about stopping any sort of incident around the Olympics.
What else are police worried about?
There are about 8,000 Muslims in the prison population, and the probation service estimates that approximately one in 10 Muslims in prison is being radicalized -- and the number's probably higher than that.
Every terror convict who's been to jail has been seen as a hero by certain aspects of their community, and while they may not commit another terror act, they will attract what are known as "clean skins" -- people who have no past terror convictions. So you have this problem where Muslims who are radicalized in jail come out and become magnets who radicalize kids in their neighborhoods, and that is a very real threat.
The other threat is from people like the Real IRA (Irish Republican Army) -- unlike al Qaeda, the Real IRA are actually building 400-lb bombs, and these bombs are getting caught and intercepted due to intelligence operations.
There's a concern that the Real IRA is getting much more sophisticated than they used to be -- the sophistication of their improvised explosive devices are getting much better, and we've heard that from a number of sources. While the Real IRA probably wouldn't want to attack the Olympics as much as a group like al Qaeda would, they're actually building big bombs in cars that are more sophisticated than what al Qaeda cells in London are capable of.