British police have arrested four men of indeterminate nationality and religion, in a plot to build a radioactive “dirty bomb:” UK Police Arrest Four in ‘Dirty Bomb Plot’.

LONDON (Reuters) - British police said Saturday they had arrested four men under anti-terrorism legislation after a tip-off from a newspaper which said the suspects tried to buy explosives for a dirty bomb.

Three of the men were arrested in a raid on a hotel in Brent Cross, north London, Friday and the fourth was seized later the same day at his home, also in north London.

“All four were arrested under section 41 of the Terrorism Act, on suspicion of the commission, preparation or instigation of acts of terrorism,” London’s Metropolitan police said in a statement.

They said they had been acting on information provided by the News of the World newspaper, which said one of its reporters had infiltrated a gang trying to buy radioactive material for a Saudi Arabian who it said might be linked to Al Qaeda.

The tabloid newspaper said the Saudi was prepared to pay $540,600 for a kilogram (2.2 pounds) of ‘red mercury’, a mysterious radioactive substance which is rumored to have been developed by Russian scientists during the Cold War.

Hmm. Saudi Arabia. That’s probably a clue.