It is the biggest occasion in the town since the funeral of King George VI in 1952.

Shortly before midday, the Queen announced she was giving her third son a new title. He will now be known as Prince Edward, the Earl of Wessex and Viscount Severn. Sophie will become Her Royal Highness, the Countess Wessex.

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Edward will also be given the Dukedom of Edinburgh after the death of the Queen and the present Duke of Edinburgh.

30,000 expected

Although there is no sign of the huge throngs which have attended other Royal Weddings, several hundred well-wishers had lined the streets of the Berkshire town on Saturday morning.

BBC reporter Damian Grammaticus said there was a "carnival" atmosphere as magicians and jugglers entertained the fans ahead of the 1700BST wedding.

One royal well-wisher waits patiently

Some had camped overnight, and were waving the Union flag, chatting and drinking champagne as they waited.

The crowds on the street are expected to swell to about 30,000 by late afternoon, while a further 8,000 members of the public have been invited into the castle precincts to see the bride and groom arrive at St George's Chapel, where the ceremony will take place.

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Meanwhile, media crews made final checks on TV cameras which overlooked Windsor High Street from every possible vantage point. The wedding is expected to be watched by millions of TV viewers around the world.

Security measures have been stepped up around the castle in case anti-monarchist protesters, who joined riots in London on Friday, should try to disrupt the wedding day.

Demonstrators had said they would hold a mini-protest in Windsor, but there was no sign of them on Saturday morning.

Windsor is festooned with flags and banners

Prime Minister Tony Blair, speaking from Cologne, Germany, where he is attending the G8 summit of the world's leading powers, said the couple had the "support and affection" of the whole country.

"Everyone likes a good wedding," he said. "I am sure everyone's delighted for them...They are a very lively, intelligent couple and the whole country will be right behind them."

On the eve of the wedding, following a rehearsal in St George's Chapel, the bride stayed with her family at Royal Lodge, the Queen Mother's private home at Windsor. Edward is thought to have stayed at the Castle.

Fevered excitement

The wedding is meant to be a relatively low-key affair, with no ceremonial state or military involvement. No politicians - not even Mr Blair - will be present, underlining the couple's wish for their day not to be a state occasion.

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The service, starting at 1700 BST and led by the Bishop of Norwich, the Right Reverend Peter Nott, will be relayed throughout the grounds of the castle, and hymn sheets will be distributed to the ticket holders.

After the service, the royal fans will get a brief chance to wish the couple well as they travel in an open carriage through Windsor to return to the castle for the reception.

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Among more than 500 guests at the event will be members of the Royal Family, Ms Rhys-Jones's family, friends and members of the royal household.

The Queen, the Duke of Edinburgh, the Queen Mother, the Princess Royal and her husband Commander Timothy Laurence, and her children Peter and Zara Phillips, are all expected to attend.

The Prince of Wales and the Duke of York are Edward's supporters - the royal equivalent of best men.

Their children, Princes William and Harry, and Princesses Beatrice and Eugenie will also be there. The Duchess of York has not been invited.

Many preparations have been taking place in and around Windsor Castle

Princess Margaret, who is still recovering from badly scalding her feet in Mustique in March, is hoping to attend but may have to use a wheelchair. Ms Rhys-Jones will be given away by her father, Christopher. Her mother, Mary, brother, David, and his wife Zara will also be there.

Other guests are to include Samantha Shaw, who designed Ms Rhys-Jones's wedding dress, and her new husband David Keswick.

Celebrities on the guest list include Prince Edward's former boss Lord Lloyd-Webber, his ex-girlfriend actress Ruthie Henshall, Stephen Fry, Billy Connolly and John Cleese.

Wedding feast

Singers Tom Jones, Michael Ball and Harry Connick Jnr have been invited, as have actors John Travolta, Charles Dance, Robbie Coltrane, Robert Powell and Michael Elphick. Sports personalities Nigel Mansell, Duncan Goodhew and Barry McGuigan are also expected to attend.

At the reception, 9,000 canap�s will be served in the Waterloo Chamber and the Grand Reception Room, before the guests move into the restored George's Hall for a buffet-style dinner.

TV cameras will be inside St George's Chapel for the ceremony

The wedding menu will consist of coulibiac - smoked haddock baked with rice and mushrooms in pastry - beef stroganoff and a selection of vegetables and salads, followed by fresh raspberries for dessert.

The cutting of the wedding cake and the toasts, made by the bride's father, the groom and the supporters, will take place before dinner.

Music at the reception will be provided by a string quartet from the National Youth Orchestra of Scotland, a brass ensemble from the London Mozart Players and the band of Her Majesty's Royal Marines.

The approximate BST timetable for the day runs as follows:

• 1330: Members of the public with tickets admitted to the precincts of Windsor Castle
• 1530: Doors of St George's Chapel open for guests
• 1630: Members of the British and other royal families start to arrive at the chapel
• 1640: Members of the Rhys-Jones family arrive at the chapel
• 1645: Prince Edward and his party are met at the West Door by the Dean of the chapel and escorted to the Bray Chapel
• 1650: The Queen and the Duke of Edinburgh arrive at the West Door, to be met by the Dean and Chapter
• 1655: The bridesmaids and pageboys arrive at the West Door, to be met by the Dean and Chapter
• 1700: Miss Rhys-Jones and her father arrive at the West Door, and the service begins
• 1745: The service finishes, and the bridal party leaves by the West Door, posing outside the door for photographs
• 1755: The bride and groom leave the chapel in an open Ascot landau carriage and pass through the castle precincts, before travelling along Windsor's High Street and Park Street, returning via the Home Park
• 1800: The reception begins in the State Apartments of Windsor Castle
• 1810: The bride and groom return to the castle
• 2000: A buffet-style dinner for guests starts in St George's Hall