LONDON - Flags are going up, cleaning crews are scrubbing down and two die-hard fans are already camping out. Welcome to Westminster Abbey, ground zero for Britain's royal wedding frenzy.

Workers were putting up flags Tuesday near the venerable abbey in central London and cleanup crews were deploying as the finishing touches were put in place.

Union flags adorn the Mall, part of the Royal wedding procession route between Buckingham Palace and Westminster Abbey in London April 26, 2011. [Photo/Agencies]

In the past days and weeks, large temporary media structures have gone up to offer standing room for thousands of journalists expected in London to witness Friday's nuptials of Prince William and Kate Middleton.

Police were getting ready too. Scotland Yard's cavalry arm was putting its ceremonial division, known as the Grey Escort, through its paces ahead of Friday's ceremony, while the military was gearing up for a dress rehearsal involving hundreds of service personnel expected to line the procession route.

Streets in London are being sealed off so troops from London's Wellington and Hyde Park Barracks can participate in the rehearsal early Wednesday morning.

Scotland Yard and other regional forces are to deploy around 5,000 officers to police the royal wedding procession, but Assistant Commissioner Lynne Owens appealed to the public to be on their guard amid fears that Irish or Islamist extremists could target the ceremony.

"We really need you to be our eyes and our ears," Owens said.

Tuesday was the last day that the venerable abbey is open to the public before the royal wedding. Dozens of tourists milling around the ancient building were asked to pause for a moment of reflection as a public prayer was offered for William and Middleton's marriage.

"Today we pray for all couples preparing for marriage, especially today we pray for His Royal Highness Prince William and Miss Catherine Middleton as they prepare for their great day on Friday," the Rev. Martin Hume said.

At a prime spot along the wedding procession route, John Loughrey of London, a 56-year-old self-described "super-fan" of the late Princess Diana, was already camped out.

"I have always been loyal to the Royal Family," he said. "Diana would be proud of her son Prince William and Catherine's marriage with Prince Harry as best man. She will be with them in spirit in Westminster Abbey on their special day and always."

Wedding fans pose for photographers outside Westminster Abbey ahead of the Royal wedding in London April 26, 2011. [Photo/Agencies]