April 19, 2011 -- Vigilant British authorities have built multiple layers of heavy security around the parade route Prince William and Kate Middleton will take for their April 29 royal wedding. The so-called "ring of steel" will guard against potential terror threats to the royal couple from Al Qaeda, anarchists and IRA splinter groups, among others.
From making full use of London's robust closed circuit television (CCTV) camera system, to dispatching hundreds of undercover police officers and even inspecting and sealing sewer drains, authorities are pulling out all stops to protect the prince, the future princess and the throngs of spectators expected to turn out for the wedding procession, officials told ABC News. Though there has been no specific threat against the wedding, bomb-sniffing dogs, hazardous material teams, riot police and roof-top snipers will be dispatched on the day of the ceremony, and foreign intelligence services will also be participating in the massive security effort, they said.
From special police command centers hooked up to the CCTV system, authorities can keep an eye on hundreds of people at once, according to British Transport Police Chief Constable Andrew Trotter.
Trotter gave ABC News an inside look at one of the command centers used for special events like the royal wedding. On the center's huge bank of monitors, operators can watch Buckingham Palace, Westminster Abbey, or zoom in on crowds to check out suspicious packages and individuals, Trotter told ABC News. A toggle switch allows extremely tight close-ups of faces in hundreds of public places all along and around the wedding route.
"I wouldn't want to operate on any major event without it," Trotter told ABC News. "I love the pictures. ... It's a great tool and there will be more and more of it."
Security officials are prepared to sift through the flood of images using "Cognitive Visual Affirmation," a sophisticated technique in which experts watch for body movements that might indicate a person could be a threat. In addition, Trotter said officers will keep using another, more traditional technique: looking for anything strange.
"It will be something that is a bit unusual, for example, people hanging around for a long time, letting trains go by before they get on. Just strange behaviors, people looking out of place," he said.
England's terror threat level has been at "severe" since January 2010. Security experts in London told ABC News the wedding has a higher threat profile than any previous royal event and regular meetings of COBRA, the British national emergency committee, have been increased recently.
And, in this case, authorities are preparing for threats from not one group, but three.
Radical Muslim Leader: Al Qaeda 'Has Their Eye' on Wedding
The high-tech police commander centers were not in place six years ago when Islamist terrorists attacked the London underground and bus system, killing more than 50 people.
Since then, authorities have arrested dozens of Al Qaeda-inspired, Al Qaeda-directed and "self-radicalized" terror suspects across the United Kingdom and disrupted what they said were many more Islamist plots.
Anjem Choudary, a London-based radical cleric and leader of the now-banned Islam4UK group, said that the royal wedding would "certainly be a target for those who want to cause havoc in Britain," including Al Qaeda.
"The Queen and her children are actively engaged in the war against some Muslims in Iraq and Afghanistan," he told ABC News. "She has actively supported the role of Britain in its policy of occupation and slaughter in her Queen's Speech, and we can see that William himself has been involved in military action in Muslim countries."
Demonstrating Muslim Group Threatens 'Nightmare' on Wedding Day
One British Muslim group linked to Choudary, Muslims Against Crusades, posted a statement on its website criticizing the royals along with a countdown clock to the wedding day.
"Unfortunately, Britain's continued interference in Muslim lands is showing no signs of abating," reads the statement. "In light of this, sincere Muslims have decided to organize a forceful demonstration."
The statement goes on to call for Prince William to "withdraw from the crusader British military," promising a "nightmare" on his wedding day should he refuse.
Though a spokesman for Muslims Against Crusades told ABC News the group is non-violent, officials said they are more concerned the vague threat could spurn violent action by other, "self-radicalized" Muslims.
Resurgence of Irish Republican Terrorism
In addition to relatively new terror threats, British authorities say they are increasingly contending with the resurgence of a decades-old foe: Irish Republican terrorism.
Irish Republicans who reject the peace deal between the Provisional IRA and the British government are believed to have been behind at least 40 significant terror attacks against national security targets in 2010. Last fall, England raised the threat of attacks by IRA splinter groups from "moderate" to "substantial."
British authorities admit they underestimated the Irish. As recently as 2007, they had viewed the terror groups as a violent handful with little to no political support.
"At that point," said Jonathan Evans, director general of MI5, Britain's counterintelligence service, in a 2010 report, "our working assumption was that the residual threat from terrorism in Northern Ireland was low and likely to decline further as time went on and as the new constitutional arrangements there took root."
"Sadly, that has not proved to be the case," said Evans. "On the contrary, we have seen a persistent rise in terrorist activity and ambition in Northern Ireland over the last three years."
Anarchy in the U.K.
Finally, authorities are also preparing for possible disruption by English anarchists including the "Black Bloc" youth who have plagued organizers of events across Europe and the U.S.
In March, large-scale protests against government spending cuts broke out into widespread violence that left windows broken, several shops damaged and around 200 protestors arrested. Authorities believed anarchists may have played a role in sparking the violent outbursts. Just days after that incident, Scotland Yard announced it was bracing for threats against the royal wedding from anti-monarchists, according to a report by the Associated Press. Other anarchist groups in Europe claimed responsibility for letter bombs sent to government buildings in both Greece and Switzerland last month.
British Security Official: It Will Be a Long Day, 'But We Hope Very Happy'
Though the potential threats are numerous, former NYPD bomb squad detective Kevin Barry said the royals have one very strong asset, beyond tight security.
"What they also have is incredible public support for the royal family and a strong 'see something, say something' attitude," he said. "They have done this before, but it has been a number of years. It's like the NYPD doing a New Year's Eve gathering."
Trotter believes his men are up to the challenge.
"It will be an exhausting day for the officers in this room," Trotter said of the men in police command. "It will be a long, arduous day, but we hope very happy day at the end of it."