The royal wedding of Prince William and Kate Middleton will be encircled by a huge security ring - enforced by police and CCTV on the ground and surveillance from the air. With more than two billion people expected to watch the wedding, disrupting the event would give any cause maximum exposure. From the moment the wedding date was announced police began digitally mapping every location from the air, giving them an accurate picture of potential weak spots, such as rooftops, Sky News reports.

"The police will be engaged in a massive security operation in the weeks leading up to the wedding," Brian Paddick, the former deputy assistant commissioner of the Metropolitan Police, told Sky News. "They will be looking at people known to have an obsession with the royals, perhaps, or people they suspect of planning a terrorist attack, to ensure that security is tight on the day."

Searches this week began at key locations, such as The Mall and Horse Guards Parade, to eliminate the risk of a terrorist strike. Officers have searched drains and opened up lampposts and traffic lights to check for explosive devices. All police leave has been suspended, ensuring there are enough resources on the ground and on rooftops on the day.

 "If you've got a particular location or potential problem or individual we want to look at, we'll put it on screen and let the control room have a look," Sgt. Richard Brandon said. "You can get detailed images of people, even number plates, and from that the control room can make a tactical decision about what to do next."