Royal wedding
Prince greets fans before wedding
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Well-wishers gather at palace
Straw surprise at wedding 'snub'
Crowds are gathering in central London for the wedding of Prince William and Kate Middleton at Westminster Abbey.
The first of the 1,900 guests will arrive from 0815 BST, with the ceremony itself getting under way at 1100.
Thousands of people have camped out overnight on the procession route the couple will take to Buckingham Palace.
William will wear the red tunic of an Irish Guards colonel - his most senior honorary appointment - but the bride's dress design is being kept secret.
The Met Office says the day will start off dry but cloudy in London but there is a risk of heavy showers developing later on.
On Thursday night, Prince William went on an impromptu walkabout to meet royal watchers who had thronged to The Mall, near the palace.
He spent several minutes shaking hands, chatting and posing for pictures telling well-wishers: "All I've got to do is get the lines right."
William spent Thursday evening with the Prince of Wales, Duchess of Cornwall and Prince Harry, while Miss Middleton and her family gathered at the Goring Hotel, in Belgravia, a short distance from Westminster Abbey.
BBC reporters at the scene estimated between 3,000-5,000 people had been camping overnight in The Mall and around Westminster Abbey, with more than 600,000 expected to line the streets by the time of the service. About two square miles of central London have been closed to traffic.
Scotland Yard says 5,000 officers will be on duty, with more than 900 along the wedding route. Most will be in uniform, but some will be in plain clothes, mixing with the crowd.
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Guide to the occasion
Schedule for the day
How to watch the day's events
Explore Westminster Abbey
Who's who at the wedding
Seating plan
Route map
Video tour of the route
London travel tips
Weather forecast
Elsewhere in the UK more than 5,500 street parties are taking place - including one hosted by Prime Minister David Cameron at Downing Street and another by the anti-monarchy campaign group Republic.
After the service, five carriages drawn by mounted troops of the Household Cavalry will carry the newlyweds, the Royal Family and the Middleton family on the 15-minute journey from Westminster Abbey to Buckingham Palace.
The route will take them past the Houses of Parliament and Downing Street and, under rows of Union Jacks, along The Mall, to Buckingham Palace, where the couple will appear on the balcony at about 1325 BST.
Royal officials said William and Kate have been involved in planning their wedding day, from the music at the ceremony to the flowers and the cake.
Inside Westminster Abbey itself, six field maples and two hornbeams will line the aisle leading up to the altar.
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William spent several minutes talking to fans on a walkabout ahead of the wedding...
Some 650 guests have been invited to the palace for a buffet lunch and about 300 close friends and relatives will stay on for formal black tie dinner and disco in the evening.
But the Queen and the Duke of Edinburgh will leave for a weekend away after hosting the lunchtime reception and will miss Prince Harry's best man speech and Michael Middleton's father of the bride address.
The Archbishop of Canterbury will conduct the wedding ceremony, which will see Miss Middleton vow to "love, comfort, honour and keep" Prince William but not to obey him.
The couple have chosen royal warrant holders Wartski to make the wedding ring for Miss Middleton. Following a long tradition of royal weddings, it has been fashioned by the Bangor-founded firm from Welsh gold given to Prince William by the Queen.
In their official wedding programme released on Thursday, the royal couple said: "We are both so delighted that you are able to join us in celebrating what we hope will be one of the happiest days of our lives.
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...as Miss Middleton and her family gathered at the Goring hotel
"The affection shown to us by so many people during our engagement has been incredibly moving, and has touched us both deeply."
Prince William's choice of a military uniform for his wedding is something of a surprise, royal watchers say. As a search and rescue helicopter pilot in the Royal Air Force, many had predicted he would wear his blue flight lieutenant's uniform.
However, as an honorary colonel of the Irish Guards infantry regiment, he has opted to wear the red tunic and forage cap, fitted by military and civilian tailors Kashket and Partners.
Prince Harry is a captain in the Household Cavalry's Blues and Royals regiment and will wear his uniform, while Prince Charles will be in his Royal Navy admiral's outfit.
The bride will walk up the aisle to coronation anthem I Was Glad, by Sir Charles Hubert Hastings Parry, from Psalm 122.
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Timetable (BST) on 29 April
1015 - The groom and Prince Harry arrive at Westminster Abbey
1051 - The bride, and her father, leave the Goring Hotel for the abbey
1100 - The marriage service begins
1230 - The bride's carriage procession arrives at Buckingham Palace
1325 - The Queen and the bride and groom appear on the balcony
1330 - Fly past by the Royal Air Force and Battle of Britain Memorial Flight
Royal Wedding timings
It was composed for the crowning of Prince William's great-great-great grandfather, Edward VII, at Westminster Abbey in 1902.