"You are just increasing the size of the haystack," Mr. Shora said. "Are you going to monitor everyone? Do we want to become a police state?

A government report on the London bombings issued last month said, "The attacks showed very clearly that terrorism is a 'homegrown' problem."

There is "a need to double surveillance and investigative capability" domestically, the report said, so that authorities can "find ways of broadening coverage to pick up currently unknown terrorist activity or plots."

"Surveillance is absolutely crucial,"

"You can't not do it,"