April 29: An extra day off for us all as William and Kate set wedding date

And the wedding - including the costs of the church service, music, flowers, decorations reception and honeymoon - will be paid for by the Royal family and the Middleton family.

The public will pay for associated costs like security.

Jamie Lowther-Pinkerton, private secretary to Prince William, said the couple chose Westminster Abbey for its "staggering beauty", 1,000-year Royal history and intimacy despite its size.

He told reporters in a briefing at St James's Palace: "The venue has long associations with the Royal family - it is in many ways the Royal family's church - and of course with Prince William personally.

"For Miss Middleton, the associations she has with the Abbey are quite simply the same as any British person would have for such a glorious and holy place."

By coincidence April 29 is the feast of St Catherine of Siena.

Mr Lowther-Pinkerton said those planning the nuptials were very conscious of Britain's precarious finances.

"All parties involved in the wedding, not least Prince William and Miss Middleton, want to ensure that a balance is struck between an enjoyable day and the current economic situation," he said.

"To that end the Royal family and the Middleton family will pay for the wedding."

He said this move drew directly from the precedent set by the Queen and the Duke of Edinburgh's wedding in 1947 and Charles and Diana's nuptials in 1981.

Mr Lowther-Pinkerton said William and Miss Middleton were "completely over the moon" about their engagement.

"I've never seen two happier people, which is absolutely fabulous to work in that sort of environment," he said.

"They're on Cloud Nine, like any other newly-engaged couple.

"They're now getting stuck into organising their wedding. They are very much in charge of the arrangements for the big day.

"They're giving us and the Household office very firm direction indeed."

Downing Street announced that the wedding day would be a public holiday.

David Cameron had already backed calls for an extra bank holiday to celebrate the occasion.

The couple announced their engagement last week, nine years after meeting as students at St Andrew's University, sparking fevered speculation about where and when they would tie the knot.

Westminster Abbey was the favourite venue to host the wedding after Miss Middleton was photographed leaving the historic place of worship in central London last week.

Sadly, the abbey was also the venue of William's mother's funeral.

As a 15-year-old boy the Prince walked behind the coffin of Diana, Princess of Wales as it was led to the imposing church in September 1997.

The French Gothic walls of the ancient church have welcomed kings and queens for more than 700 years and it is the final resting place of 17 monarchs.

Prince William's grandmother, the Queen, and great-grandmother, the Queen Mother, were both married at Westminster Abbey.

The first ceremony at the the Abbey saw William I crowned King on Christmas Day 1066, and the current Queen took her seat on the coronation chair in a televised ceremony in 1953.

Many Royal weddings have been held at the Abbey during the 20th century.

The Queen's parents, Prince Albert - later George VI - and Elizabeth Bowes-Lyon, the Queen Mother, exchanged their vows there in April 1923.

And the Queen, then Princess Elizabeth, married Lieutenant Philip Mountbatten, later the Duke of Edinburgh, on November 20, 1947.

It was a morale boost in the tough post-war years and millions of people listened to the ceremony on the wireless.

But some other Royal weddings held at the Abbey have been less happy.

Princess Margaret, the Queen's sister, married Antony Armstrong-Jones, later Earl of Snowdon, at the church in May 1960. Their marriage was dissolved 18 years later.

The Princess Royal wed Captain Mark Phillips in November 1973. Their marriage was dissolved in April 1992.

The Duke of York walked down the Abbey's aisle with Sarah, the Duchess of York, when they were married in July 1986. The pair divorced 10 years later.

William and Miss Middleton are "calling the shots" on the wedding plans but have a "rather large supporting cast" to put them into action, the Prince's private secretary said.

Mr Lowther-Pinkerton added: "We know that the world will be watching on April 29, and the couple are very very keen indeed that the spectacle should be a classic example of what Britain does best."

William has requested that as far as possible members of the armed forces involved in the wedding should be drawn from those already on ceremonial duties to ensure personnel are not taken off operations or training.

Mr Lowther-Pinkerton said: "Prince William and Catherine have made it very clear that they wish everybody to be able to enjoy the day with them.

"Consequently the day will be a proper celebration for the nation and the realms.

"Having said that, the couple are very mindful of the current situation, and for example Prince William has already expressed a clear wish that any involvement by the armed forces should rely in great part on those servicemen and women already committed to public and ceremonial duties."