An image of Prince William and his soon-to-be bride Kate Middleton is seen on a souvenir in London April 27, 2011.[Photo/Agencies]

Prince William and Kate Middleton attended their final wedding rehearsal at Westminster Abbey on Wednesday as the armed forces, media organizations and spectators prepared for the couple's big day.

Roads in central London around Buckingham Palace and along the route of Friday's marriage procession from the abbey were closed from early morning as about 1,000 members of the military held a full-scale practice.

Carriages that will carry members of the wedding party also took part alongside mounted cavalry.

William and Middleton arrived in a fleet of vehicles that swept into the abbey grounds for their rehearsal on Wednesday evening.

They were accompanied at the run-through by William's brother and best man Prince Harry, the Middleton family and senior clergy, a spokesman for the couple said.

Across the capital, bunting has gone up and flags are beginning to be hoisted, with similar preparations around the country where about 5,500 street parties will be held.

A small army of media from around the world has descended on makeshift studios set up outside Buckingham Palace and along the route to cover the ceremony that one British minister predicted would attract a global TV audience of some 2 billion people.

"America and the world is really excited about a piece of great news," said Linda Bell Blue, executive producer of U.S. entertainment news programme Entertainment Tonight, who is heading up a team of 70 staff for the wedding.

"It's been a pretty rough time around the world -- in the Middle East and in Japan and the world economy -- and this is something to be happy about," she told Reuters.

"Americans love a big production. This is the Oscars on steroids. Its the pageantry, the enthusiasm, it's about what people are wearing."

Some royal fans have already begun camping outside the abbey to secure the best spots to watch Friday's events, and hundreds of thousands of people are expected to start arriving in London.

MORE THAN A MILLION VISITORS

VisitBritain, the national tourism agency, is predicting an extra 600,000 tourists in the capital on the day, meaning there would be a total of some 1.1 million visitors with 40 percent of those coming from abroad.

"That could bring anything up to 50 million pounds ($83 million)," a spokesman said, adding the number of in-bound flights to Britain for the weekend had risen by 244 percent.

London and Partners, the agency which promotes the city, said it expected there would be 600,000 people actually lining the streets, the same number as came to watch the 1981 wedding of William's parents Prince Charles and Princess Diana.

British Prime Minister David Cameron has said the occasion would be a boon to a nation coping with government austerity measures which have resulted in drastic spending cuts and job losses.

"People across the country, and indeed across the world, are getting excited about the events on Friday," Cameron told parliament.

Archbishop of York John Sentamu, the second most senior cleric in the Church of England, echoed those sentiments.

"This event I hope will give a lot of hope to a lot of people, particularly young people," he said in a TV interview published on his website.

Those who do go to London to watch the procession or camp out could be in for a cold and wet experience, with weather forecasters predicting showers and a brisk wind.

On Tuesday, police appealed to the public to help them spot any potential troublemakers, while promising that they would not tolerate any attempt to disrupt the event.

Some 5,000 police officers will be on duty to deal with potential threats ranging from international Islamist militants to anarchists and stalkers.

Meanwhile the one-and-a-half mile processional route has undergone a deep clean to get it looking spic and span.

A team of 130 street cleaners including 80 sweepers along with 30 vehicles are being lined up to deal with the 140 tonnes of waste expected to be left by those watching on Friday.