Four men arrested on suspicion of terrorism at a north London hotel are being quizzed by police for a fourth day.
The men can be detained until October 1st after an extension was issued under the Terrorism Act yesterday.
Three of the men were arrested in a "pre-planned" operation by officers from the Metropolitan Police's anti-terrorist branch at a hotel in Brent Cross on Friday. Another man was arrested at his north London home.
They were arrested under section 41 of the Terrorism Act, on suspicion of the commission, preparation or instigation of acts of terrorism.
A Scotland Yard spokesman said: "All four men have been taken into custody at a central London police station for further questioning.
"Several addresses have been searched. Some searches continue." Police officers were "acting on information received from the News of the World".
The newspaper has said it had uncovered a plot to buy radioactive material for a dirty bomb.
It claimed an undercover reporter posing as a Muslim extremist discovered a Saudi sympathetic to "the Muslim cause" who was willing to pay £300,000 (sterling) for a kilo of powerful radioactive red mercury.
The chemical is said to have been developed by Russian scientists for "briefcase nuclear bombs", although scientists are divided over whether any actually exists.
Earlier this year, security agents in the southern city of Odessa in the Ukraine arrested two Middle Eastern men and seized 24lbs of a substance identified as "red mercury".
According to the News of the World, meetings were held with gang members hoping to supply the radioactive material to their Middle Eastern buyer.
The journalist was allegedly told the chemical would be used either "here in the UK or the USA". The paper contacted Scotland Yard, and a final meeting was arranged at the Holiday Inn in Brent Cross on Friday.
PA