With a month to go before Prince William and Kate Middleton marry, excitement about Britain's biggest royal wedding for 30 years is building as details emerge, although the dress remains a state secret.

The second-in-line to the throne marries his university sweetheart on April 29 at Westminster Abbey, in an event that has become a global media sensation ever since they announced their engagement last November.

A month away, the invitations have gone out, the cake has been chosen, the carriage booked and the music for the church service settled.

William has already held his stag night, royal officials said Monday, although they refused to divulge what Kate had planned to mark the end of her days as an unmarried woman.

Around them, public excitement is building both in Britain and abroad, where many see William and Kate as a breath of fresh air for the monarchy.

"This is something that a lot of people are really looking forward to," said Max Clifford, a leading public relations consultant.

The excitement is particularly frenzied in the United States.

"In America, it's crazy," said Robert Jobson, royal commentator and author of "William and Kate: The Love Story", saying one US TV network was interviewing him three times a week about the royal nuptials.

Although the British have been a little more cool on the event, he believes enthusiasm will quickly begin to mount in the coming weeks as more details emerge of the wedding and the couple's appearances increase.

"We always like in Britain to not get overly excited and try to make out we're not having fun, and then when it actually happens the whole place will be mobbed and everyone will be drunk and having fun," he told AFP.

An extra 600,000 tourists are expected to flock to London for the event, according to Visit London, the capital's tourism body.

An Internet search reveals there are still hotel rooms available in the city on those days, but in case of a last minute rush, a makeshift campsite will be set up on Clapham Common in south London.

The couple are to marry in London's historic Westminster Abbey, in Britain's biggest royal wedding since William's parents Prince Charles and the late Princess Diana married in 1981.

Kate, 29, will arrive in a Rolls-Royce limousine and it is only when she steps into the Abbey that her dress will be revealed to a predicted global television audience of one billion.

Palace officials are treating all details of the gown as a state secret, although reports suggest the successor to the late fashion designer Alexander McQueen, Sarah Burton, has been given the coveted commission.

Archbishop of Canterbury Rowan Williams will preside over the ceremony in front of 1,900 guests, including foreign royals, family and friends, although only 600 will be invited to a reception at Buckingham Palace afterwards.

British servicemen wounded in Afghanistan and football star David Beckham and his wife Victoria are thought to be among those on the guest list.

The historic abbey will reverberate to the sound of two choirs, the London Chamber Orchestra and two fanfare teams from the Royal Air Force and the Household Cavalry.

Afterwards, the newlyweds will travel back to Buckingham Palace through the streets of the capital, lined with what is expected to be huge crowds taking advantage of a public holiday to wish the couple well.

As Britain struggles with the aftermath of the recession, the royal family and the Middletons will share the wedding costs, with the government meeting security and transport costs.

Many hope the wedding will provide an economic boost - according to consultants Verdict, the wedding is set to inject an extra £620 million ($995 million, 705 million euros) into the British economy.