UK drops terror alert level to lowest in 2 years

The government did not explain its decision to downgrade the threat from "severe," which Britain's domestic spy agency MI5 describes on its Web site as a "high likelihood" of future terror attacks" to "substantial," which means that such an attack remains a "strong possibility."

Terror experts were divided on the thinking that lay behind the change.

Bob Ayers, a London-based former U.S. intelligence officer, said officials may have reduced the threat level in an effort to show that the war in Afghanistan — where British soldiers are engaged in an increasingly bloody fight with Taliban rebels — is helping keep the country safe from extremists. But he said the move sat uneasily with dire warnings voiced last year that British security services were tracking 2,000 people and dozens of suspected terrorist plots.

"Where did they go? Have they just disappeared?" Ayers asked.

Paul Wilkinson, a terrorism expert at the University of St. Andrew's in Scotland, rejected suggestions the move was politically inspired, saying Britons should treat the downgrade as a "very cautious, very tentative reduction" which could be reversed at any time.