FASTER, PLEASE: U.K. Police Make ‘Significant’ Arrests in London Terror-Attack Investigation.

Mark Rowley, the U.K.’s top counterterror policeman, said in a morning press conference that there was no evidence of further threats but that investigators were trying to determine whether the attacker acted on his own or had accomplices.

“Our determination is to understand if either he acted totally alone, inspired perhaps by terrorist propaganda, or if other people have encouraged, supported or directed him,” he said.

With the two overnight arrests, nine people were now in custody, and one woman was released on bail overnight, he said. Police have seized 2,700 items from searches, including what Mr. Rowley described as “massive amounts” of computer data.

The question is whether an attack at the heart of British government will be enough to shake Britain loose from her cultural complacency.