Scotland Yard is bracing for all types of security threats to the royal wedding _ threats that range from terrorists and anarchists to anti-monarchists and other protesters.
The declaration Monday came after rogue groups disrupted a peaceful demonstration Saturday against Britain's harshest spending cuts since World War II. About 250,000 protesters flooded London, but small groups broke away, hurling ammonia-filled light bulbs, paint and wooden planks at officers and smashing windows near Trafalgar Square. Over 200 people were arrested.
Similar groups attacked a car carrying Prince Charles and his wife, Camilla, during student protests in December.
Police commander Bob Broadhurst said Monday the April 29 wedding of Prince William and Kate Middleton at London's Westminster Abbey carries even more of a security threat than the anti-austerity protests. Since the event has special security implications, U.K. police will be able to use special stop-and-search powers that fall under Britain's counterterrorism laws.
"They won't get away with it," Broadhurst told BBC radio Monday. "The royal wedding has a different tenor to it. It's a security operation largely."
British security officials have said there is no specific terror threat to the wedding, but they are monitoring chatter over the Internet and other channels. U.K. police were criticized Monday for being too slow to realize what some of the protesters over the weekend were planning.
Police will be confronted by a myriad of security concerns at the royal wedding, including a general terror threat and crowd control for tens of thousands along a route that snakes through central London. They will be checking vehicles for explosives and looking for snipers on rooftops or amid crowds. They also need to decide whether or not to search the estimated 1,900 guests going into the Abbey or passers-by, and whether to allow protests nearby.
Only a fraction of Britain's police carry firearms. Last year, a terror tip sparked concerns that gunmen could wage Mumbai-style attacks in a European capital. The 2008 Mumbai shooting spree killed 166 people and paralyzed India's business capital for days.
"The (U.K.) terror threat is currently at severe but if we know of a specific plot likely to occur it could be raised to critical," a British security official said, speaking on condition of anonymity because of the sensitivity of his job. He declined to discuss specific threats.
All of Britain's security agencies will be comparing intelligence in the run-up to the wedding: the MI6 with its foreign intelligence, the MI5 for domestic security and the GCHQ, the country's eavesdropping agency.
Some protesters used Twitter and other social media sites over the weekend to promise more mayhem on the day of the wedding. Anti-monarchists also said they plan to have a presence near the Abbey next month.
"You're looking at a different type of threat," Broadhurst said, calling the threat to the royal wedding, "a threat to democracy."
Britain's government has pledged to scrap a law that bans any unauthorized protest within about half a mile (0.8 kilometers) of the Houses of Parliament _ which includes Westminster Abbey _ but it is likely to be several months before the rule is actually dropped.
Lawmakers are now debating a bill that proposes loosening oversight of protests and suggests curbing police powers to conduct random searches. Until the bill is passed, however, ministers will have the power to ban protests along much of the wedding route _ or to limit the size, duration and noise levels of any planned demonstration.
Last year, MI5 director Jonathan Evans warned that IRA dissidents could also mount attacks in England for the first time since August 2001, when a car bomb damaged a shopping center in London's western suburbs and injured 11 people.
Prime Minister David Cameron's spokesman Steve Field said Monday that police will provide adequate security for the wedding.
"We need to learn the lessons as we go and make sure we have the right arrangements in place, and that's what we will do in the case of the royal wedding," Field said.
A security barrier will be erected around Westminster Abbey but police say it's too soon to say whether wedding guests or passers-by will be searched. Police make security recommendations to the royal family.
Associated Press writer David Stringer contributed to this report.