When Prince Charles and Diana married three decades ago, Alan Bell was around the corner from London's Westminster Abbey in a parking lot.
He and other members of Britain's counterterrorism team were "all tooled up and ready to go," Bell recalled. If any weapons showed up in the crowd, or if the IRA called to say they were going to blow something up, Bell's group would launch a counter-assault.
A generation later, Britain's security apparatus is working in overdrive to make sure the odds of anyone attacking the wedding of Prince William and Kate Middleton are as remote as possible.
But a lot has changed in the years since Britain's last major royal wedding. The IRA tended to attack infrastructure and spare people. And while Irish dissidents remain a threat, Bell said radicalized Muslims in the country could present more of a problem.
At Charles' and Diana's wedding, Bell said spectators weren't searched by police if they were far enough back in the crowd, and few barriers were set up for crowd control except along the wedding procession route.
Fast forward to 2011, and security personnel are expected to set up concentric rings of security around Buckingham Palace and Westminster that ripple out across much of West London.
"It's different now," said Bell, who left the British forces after 22 years and today runs a security consulting firm. "You've got people who don't mind dying. You've got people whose sole aim is to kill multiple amount of people in one attack."
The U.K. Home Office says the threat level from international terrorism in Britain is "severe," which is the agency's second highest rating and means an attack "is highly likely."
Meanwhile in Washington, the U.S. Department of Homeland Security has issued a travel alert over what it calls a "high level of terrorist threat" that's due to expire the day after the wedding.
Experts say street protests are another concern. Britain is in the midst of deep government cost-cutting to manage the country's hulking debt, and the high expense of a royal wedding could make it a target for demonstrations.
Last December, when the car driving Prince Charles and his wife, Camilla, was attacked by protesters angry about drastic hikes in university tuition, it raised questions about whether British authorities were capable of protecting the royal family in such situations.
Police said they thought the driving route was safe. But after a driver picked up the couple in a Rolls Royce, a group of student protesters surrounded the vehicle.
When the confrontation was over, the car had been splashed with paint, one of its windows had been smashed and a protester had managed to poke Camilla with a stick. It was considered one of the most serious security breaches to affect the royal family in recent years.
Adding up the cost
While British Prime Minister David Cameron has said that the royal family will pay for the wedding ceremony, the government is picking up the tab for security and transportation.
Estimates of the security costs alone reach as high as US$33 million, which would make it the most expensive such operation in British history. Adding to the cost, Cameron has declared April 29 a national holiday, meaning that thousands of police officers deployed to the wedding will be earning double-time.
But the full expense may be hard to pin down, according to Fred Burton, a former American counterterrorism agent who was in charge of protecting the royal family during their visits to the United States in the 1990s.
The British government "may not be in a position to budget for something like this," he said, because security planning will likely have begun secretly long before the wedding date was announced in November.
"The average person watching this on TV or listening to it on the radio really has no idea of the scope and the degree of intelligence-related work that's taking place behind the scenes," he said.
Burton, who's now a vice-president with global intelligence firm Stratfor, added that the massive security and intelligence operation should make it "very improbable" that anything nefarious will happen at the wedding.
But that doesn't mean British authorities have an easy road ahead.
As Bell put it: "This is a security guy's nightmare."
