More details forthcoming - I was studying for finals when I noticed a crawl across the bottom of the screen (volume is muted.)

4:47 UPDATE:

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Police say they have arrested 13 people in anti-terrorism raids around Britain.

The men, in their 20s and 30s, were detained in Luton, Lancashire, Hertfordshire and in London.

The suspects are believed to have been under surveillance for some weeks.

They have been arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism.

The men will be brought to a central London police station and interviewed by officers from the Met's Anti-Terrorist Branch.

The operation is part of continuing and extensive inquiries by police and the Security Service into alleged international terrorism.

Officers from the Met's Anti-Terrorist Branch were supported by officers from Hertfordshire, Bedfordshire and Lancashire.

The BBC still just has the breaking news banner I posted above with no other details.

Police conducted anti-terrorism raids in London and several towns Tuesday, arresting 13 people believed involved in preparing terrorist acts.

London's Metropolitan Police said the afternoon and evening arrests were "part of a pre-planned, on-going intelligence-led operation."

They said men were detained "on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism," but did not elaborate.

The police said the arrests were in northwest London, suburban Hertfordshire and Bedfordshire and in Lancashire, northwestern England. Detectives were searching homes in all those locations, police said.

The suspects, who are all in their 20s and 30s, will be brought to a central London police station for questioning by anti-terrorism officers, police said.

"Today's operation is part of continuing and extensive inquiries by police and the Security Service into alleged international terrorism," the police statement said.

The current BBC story has nothing new from any of the other reports.

Other news stories:
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Earlier, Britain resisted calls to match the United States' high state of alert after warnings that al Qaeda bombers might strike and played down concerns of an immediate security threat.

On Monday, the United States increased security and increased the nation's alert to "High," prompted by Pakistan's capture of a suspected al Qaeda computer expert which yielded documents, computers, surveillance reports and sketches.

A British police spokesman declined to say if there was any link between intelligence from Pakistan and the raids....

...The police said searches were continuing and were expected to take "some time" to complete.

The operation was part of extensive inquiries by police and the security service into alleged international terrorism, the police said.

A Metropolitan Police spokesman said the suspects would be brought to a central London police station for questioning.

Officers are continuing to search "residential premises" in London and the three counties where the arrests were made.

The police spokesman said they were expected to remain at the sites for some time.

Eyewitnesses in Blackburn told the BBC they had seen the arrests of two young men.

Ruth Lazell said she had been alerted by the sounds of voices in the street outside her Preston Old Road home.

She said: "I heard a man shouting and went outside to see what was going on. As I got out of my door a policeman told me to get back inside."

Mrs Lazell said she had seen armed officers force one man to the floor and pull a second from a car, handcuffing him on the ground.

Another neighbour, who did not wish to be named, told BBC News Online she had seen a number of officers, some in flak jackets and others in plain clothes.

She said the men had been dressed by police in white paper suits and their hands and feet covered with plastic bags before they were driven away.

Resident Pearl Bernasconi told the BBC she had seen forensic officers pore over the gold Mercedes car from which the suspects were pulled.

The police said the arrests were in north-west London, suburban Hertfordshire and Bedfordshire and in Lancashire, north-western England. The Lancashire raid was in the town of Blackburn and the Hertfordshire arrests were in Luton, police said....

...Police would not say whether today's raids were linked to the Pakistani discovery, but noted that the investigation leading to the arrests had been underway for some time.

While British authorities say the threat from terrorism remains high, they have not warned of any specific threat along the lines of that announced America.

Police will have up to two weeks to hold the men before deciding whether to charge them.

Suspects arrested in previous anti-terrorism raids have often been released without charge before the two weeks expired.

The spokesman said the plan for the arrests "predated the weekend just gone", suggesting they had nothing to do with recent publicity about possible threats to London's financial district.

6:27 UPDATE: Sky News has produced the below map of the locations involved:

The suspects, who are all in their 20s and 30s, will be brought to a central London police station for questioning by anti-terrorism officers, police said. They declined to specify the men's nationalities.

7:30 UPDATE: BBC reports have been updated. I edited one of the previous BBC reports quoted so it matches their updated one, specifically concerning the identity the make of the car previously described.

The timing of the raid has also been questioned.

Cross-posted at Backcountry Conservative.