Without an heir, is divorce in the air for sad princess?

Several magazines say that, after 13 unhappy years in the Imperial Palace, the Harvard-educated former diplomat is looking for a way out of her marriage to Emperor Akihito's son, Crown Prince Naruhito. The Imperial Household dismisses the speculation.

The 42-year-old princess has spent the past two years largely out of public sight and has been diagnosed with a mental disorder that many blame on her struggle to produce a male heir.

The princess came under intense palace pressure to have another baby after giving birth to her only child, Aiko, in 2001. Her subsequent illness has sparked a succession crisis and forced the government to begin revising the Imperial House Law, which prevents females from ascending the throne.

A government panel has recommended changing the law and polls suggest that the public supports the idea of an empress. But, with just over a month left before the revision is sent to parliament, the plan has run into opposition from conservatives, including members of the ruling Liberal Democratic Party (LDP).

The former prime minister, Yoshio Mori, and the head of the LDP's Diet Affairs Committee, Hiroyuki Hosada, warned recently that the succession issue could "split the country" if handled badly. "Opposition is growing. The situation is precarious," Mr Hosada said.

The Association of Shinto Shrines, which has traditionally harvested votes for the LDP, has warned that it will withdraw support from anyone who votes for the bill, a potentially serious threat to the Prime Minister, Junichiro Koizumi, who supports a female emperor. Opponents were galvanised on Wednesday by a Tokyo rally at which more than 170 Diet members signed a cross-party petition opposing the legislation.

At least one member of the imperial family has told the government not to buck tradition. The emperor's cousin, Prince Tomohito, believes that the imperial bloodline should not be diluted by "outsiders". "There is no need to change the law," said the prince.

The speculation about Masako's state of mind has gathered pace as the debate on the succession issue heats up. "There are very few people who actually say the words divorce, but they think it," said Yagi Hidetsugu, a professor at Takasaki Keizai University. "Her withdrawal from the imperial family would certainly solve a lot of problems."