The couple have lost none of their popularity in Britain and abroad 12 months after their fairytale wedding drew cheering crowds and two billion TV viewers, with one royal expert crediting them with "saving the monarchy".

But fans are still awaiting word that they are expecting a baby, and the former Kate Middleton appears to have bucked a royal trend.

Royal biographer Andrew Morton told AFP a year ago: "If Kate is not pregnant in the next nine months, she'll be defying 200 years of royal tradition."

Press speculation has been feverish and bookies are offering narrow odds on a new arrival in 2013, while succession rules were changed last year so that any daughter of the couple would be equal with boys in the queue for the throne.

But the second in line to the throne and his wife -- who took eight years to marry and have also flouted royal convention by opting against household servants -- have made it clear they will not be bound by any timetable.

"William has said he'll take things one step at a time," royal writerRobert Jobson told AFP.

"But Kate, at 30, I'm sure she wants to start a family as soon as she can. She's been with this man for eight years of her life, she's clearly in love with him."

Since their wedding the Duke and Duchess of Cambridge, as they are now known, have triumphantly toured Canada and California, met the Obamas, made polished public appearances, and won fans from Nicole Kidman to Snoop Dogg.

Catherine, the middle-class girl made good, has become a fashion trendsetter and appeared with her socialite sister Pippa on Time magazine's list of the world's 100 most influential people.

She has also won the endorsement of Queen Elizabeth II, who has twice appeared with Catherine -- still known to many as Kate -- in public and has reportedly written to the pair to thank them for their work.

William took part in a daring rescue of two sailors in his job as a search-and-rescue pilot, and won hearts by giving Kate a cocker spaniel, Lupo, to keep her company when he was deployed for six weeks to the Falkland Islands.

Like William's mother Diana, the pair are seen as willing to get their hands dirty for good causes. But they are also credited with helping the family move on from Diana's 1997 death in a car crash and her earlier very public divorce.

"Their story has put the monarchy back on the map in terms of what they represent. They have saved the monarchy in the public imagination," Jobson said.

The pair will celebrate their anniversary on Sunday "privately", a spokeswoman said, ahead of public appearances for the queen's diamond jubilee in June and a joint trip to Singapore, Malaysia, Tuvalu and the Solomon Islands.

In 2013 they are due to move from their home on the Welsh island of Anglesey near William's Royal Air Force base to grander accommodation -- Princess Margaret's old apartments in London's Kensington Palace.

This is widely expected to accompany them starting a family, Jobson said, and will inevitably herald even closer public attention.

Their few critics have accused the pair of being "bland" and showing little personality in public, in contrast with the fizz of William's younger brother Prince Harry, who won over hosts in the Caribbean in March with practical jokes and a comical 'race' against Usain Bolt.

But Jobson noted that there is more to Catherine "than meets the eye", recalling that she originally attracted her prince's attention by "sashaying down a catwalk at university in a see-through dress".

"William and Kate understand the seriousness of the role that lies ahead of them. They don't want to put a foot wrong and they're very cautious, perhaps too cautious.

"They're aware that the future of the monarchy is on their shoulders," he said