SHE may be Prince William's girlfriend and the favourite new topic of British royal watchers, but it will take a royal engagement for Australian women's magazines to get excited about Kate Middleton.

Middleton spent her 25th birthday today under siege by paparazzi amid speculation of a marriage proposal from the future king of England.

Rupert Murdoch's News International media group, publisher of Britain's biggest circulation tabloid The Sun, has banned its mastheads from printing paparazzi images of Middleton.

A journalist from the same company's News of The World pleaded guilty last year to a plot to tap the private telephones of royal family members.

Regardless, worldwide interest in the possible future Queen has soared.

But the editors of Australia's leading weekly women's magazines said in this country Middleton would remain in the shadow of Tasmanian-born Crown Princess Mary of Denmark.

Until, that is, there is an official engagement.

"As soon as an actual engagement takes place, which I think is inevitable now, the excitement will hit Australia and her popularity will take shape,'' New Idea editor Robyn Foyster said.

Woman's Day editor Alana House said press interest, especially in the United Kingdom, has been heightened by William and the fashion-savvy Kate's reluctance to pose in public.

"Our readers love a princess, but at the moment she hasn't been spotted on a red carpet or been to a spectacular ball where she could be seen as glamorous,'' House said.

But once it's official that she could be the next Queen of England, things will change.''

While the British royals of today don't attract the same fascination of 10 years ago, when Prince William's mother Diana died in a car crash in Paris, Middleton is said to represent the ideal modern royal.

"She's very down to earth, a symbol of the royal families new attitude to marriage and a lifestyle and fashion sense which reflects the times, much like Mary,'' House said.

Obvious comparisons are being made between Middleton and Diana, who experienced a similarly rabid paparazzi before her 1981 engagement to William's father Prince Charles.

"The difference is Diana came during a time of transition where old fashioned values were still expected, Kate will be allowed to be herself,'' House said.

Foyster said Middleton, should she and William become engaged, "could potentially be as popular as Diana''.

"She hasn't really put a foot out of place,'' she said.

"With it being 10 years since Diana's death, there is a real sense of nostalgia as well.

"The prospect of a year in which there could not only be a proposal but a marriage, is very exciting.''