Royal baby: Kate in labour and admitted to hospital

The news that "the Great Kate Wait" - as bored journalists have dubbed their vigil outside the hospital - was finally over was announced in a brief statement from Kensington Palace at 7.30am after rumours began circulating that Kate had been spotted.

The statement read: "Her Royal Highness The Duchess of Cambridge has been admitted this morning to St Mary's Hospital, Paddington, London, in the early stages of labour.

"The Duchess travelled by car from Kensington Palace to the Lindo Wing at St Mary's Hospital with The Duke of Cambridge."

Kate is planning to have a natural birth and a spokesman added that "things are progressing as normal".

The Duchess is being tended by a top medical team led by the Queen's former gynaecologist Marcus Setchell, who delivered the Countess of Wessex's two children.

Assisting him is Alan Farthing, the former fiance of murdered TV presenter Jill Dando, who is the Queen's current gynaecologist.

The world's press have been camped outside St Mary's in Paddington for days in anticipation of the birth and even the Queen has joked about the imminent arrival of the newest member of her family, saying she hoped the baby was born before she went on holiday later this week.

The hospital's Lindo Wing is a private obstetric unit, with prices starting at just under £5,000 for a normal delivery package over 24 hours, with consultants' fees around £6,000 extra depending on the care required.

The Duke and his younger brother, Prince Harry, were born in the Lindo Wing and the Prince and Princess of Wales famously posed on the building's steps in 1982 holding baby William in turn.

William had taken annual leave to be with his wife last week, but is now on two weeks' paternity leave from his job as an RAF search and rescue helicopter pilot.

It is not known how long the Duchess will take off from her royal duties to care for her first child.

The new royal baby will be the Queen's third great-grandchild and is destined to be crowned monarch.

It will be the 43rd sovereign since William the Conqueror if, as expected, it follows reigns by Charles then William.

The royal couple do not know the sex of their baby but the Duke is known to want a daughter while the Duchess is hoping for a son.

When Kate met Guardsman Lee Wheeler, 29, during a a St Patrick's Day parade in Aldershot, Hampshire, she told him she did not know the sex of her baby.

The soldier said: "I asked her: 'Do you know if it's a girl or boy?', and she said: 'Not yet'.

"She said: 'I'd like to have a boy and William would like a girl'. That's always the way."

Recent changes to the rules of succession mean if a girl is born she will not be leapfrogged by a younger brother at a later date.

The sex of an infant in direct line to the throne no longer determines whether he or she wears the crown.

Betting on the name of the royal baby, which will be third-in-line to the throne, has produced one favourite with a number of bookies - Alexandra.

Many punters believe William and Kate will have a girl and have put their money on the name.

Other monikers that have attracted royal fans include Charlotte, Diana, Elizabeth and Victoria, with George and James picked by those who think the new baby will be a boy.

Soon after the royal couple arrived at the hospital wing a strong police presence was seen around the building with two officers guarding the main entrance.

But among the dozens of broadcasters, photographers and journalists were royal fans who had a ringside view of events.

Carly Gargett, 31, an event manager from Sydney, Australia, who lives in London, visited the hospital on her way to work.

She said: "I don't think I'll be doing a lot of work today, I have the royal baby cam live feed to my phone, I am so excited.

"And Kate is handling it all in such style as always - it can't be easy with the eyes of the world on her."

In centuries past the nation would not have been told a royal had gone into labour.

This is something that would have been unthinkable when the last granddaughter-in-law of a reigning queen to give birth to a future monarch did so in the 1890s.

George V's wife Mary of Teck, who was then the Duchess of York, had the future Edward VIII in 1894 and the future George VI in 1895, but news of her "confinement" was limited.

Dr Judith Rowbotham, a social historian at Nottingham Trent University, said: "Pregnancy was not something that was publicly talked about then. It wasn't discussed. It was indelicate."

David Cameron said: "Best wishes to them, a very exciting occasion and the whole country is excited with them. So, everyone's hoping for the best."

Speaking later on BBC Radio 4's Woman's Hour he said had been "pretty involved" in the birth of his children.

"It's up to every family to work out how they want to do these things," he added.

"I can't claim any role in this one, I'm afraid, except one small thing - well, it's a big thing actually - which is to get all of the heads of the realms over which our Queen is Queen, to agree that whatever the sex of the baby that Will and Kate have, if it's a girl, it will be our Queen."

The Prince of Wales, who will become a grandfather for the first time when Kate's baby is born, was quizzed about the birth as he visited the National Railway Museum in York to mark the 75th anniversary of the Mallard locomotive.

Asked by Sky News if he knew anything about the the birth, he replied: "Absolutely nothing at the moment, we're waiting."

A spokesman for Imperial College Healthcare NHS Trust, which runs St Mary's Hospital, said: "During her stay at the hospital, the Duchess is being cared for by an expert team of consultants and midwives.

"It goes without saying that the whole trust wishes her well and we are exceptionally proud that the Duke and Duchess of Cambridge have chosen to have their baby here."

TV presenter and adventurer Ben Fogle's pregnant sister Tamara is also in the Lindo Wing.

She has not had her baby yet.

Fogle said: "It is a very exciting time, which I suppose is easy for the husband to say. We don't have to go through the pain."