Japan's Imperial Family faces a crisis of legitimacy because of growing discontent with the absence from public life of Crown Princess Masako, senior courtiers in the Imperial Palace fear.

Five years after she gave up public duties because of depression, sympathy for the Princess's plight is giving way to scepticism about the seriousness of her condition - and to anxiety about what her continuing indisposition will mean for the monarchy when her husband, Crown Prince Naruhito, succeeds to the Chrysanthemum Throne.

For the first time respectable commentators are openly discussing what was once unthinkable: the possibility of an imperial divorce.

The crisis will be brought into focus next week with the visit to Japan of the Prince of Wales and the Duchess of Cornwall. “Royal families around the world can no longer take for granted their legitimacy,” a palace source said last week. “In the 125th generation [of the present Emperor Akihito and Empress Michiko], legitimacy is earned through hard work and humility. But we worry about the 126th generation.”

When the Princess ceased her official duties abruptly in 2003, the Imperial Household Agency (IHA) first announced that she was suffering from shingles. When The Times reported that she was also being treated for depression, the IHA denounced the article as indecent - only to confirm two months later that she was suffering from an “adjustment disorder”.

The public reaction was one of sympathy for the Princess, who gave up a career as a diplomat to marry Prince Naruhito in 1993. She struggled to conceive a child and, after undergoing fertility treatment, suffered a miscarriage. The couple's only child, Princess Aiko, was born in 2001 but, as a girl, is ineligible to ascend to the throne. The birth of a boy to the Crown Prince's younger brother in 2006 solved the succession problem for the time being and eased some of the pressure on Masako. She still carries out very few official duties on the grounds that doctors have advised against it.

However, in the past year especially, she has made numerous outings from the Crown Prince's official residence, the Akasaka Detached Palace.

She has been photographed dining at expensive Chinese, Mexican and French restaurants and attending events at her daughter's school. More and more openly, the usually restrained Japanese media are speculating that the problem is not so much depression as a straightforward dislike for onerous public duties.

Next week, for example, Naruhito and Masako - both British-educated - will give a private dinner party for the Prince of Wales and the Duchess. But next month, when King Juan Carlos and Queen Sofia of Spain are on a six-day visit, Masako will not make an appearance. “What logical explanation can we give for that?” a palace insider asks. “That the British are healthy but the Spanish make her ill?”

In May a magazine ran an article by Kanji Nishio, a right-wing academic and champion of the Imperial Family. He urged that Princess Masako's family “take her back” - a euphemism for divorce - because of the damage that she is doing to the Imperial Family. “The members of the Imperial Family are the passengers of the ship named the Imperial System, but not its owners,” he wrote. “If one individual gets seasick and cannot stay on board, then there is no alternative but to disembark.”

The article boosted the circulation of the magazine, Will, from 100,000 to 150,000 a month and drew many e-mails, letters and telephone calls, most of them in agreement with Professor Nishio. “Nishio has started a debate that people with common sense want to participate in,” Tomoko Seo, an editor at the magazine, said. “People are frustrated and angry with Masako for making many private outings, although she cannot carry out official duties.”

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