Hong Kong: Britain said on Friday a Hong Kong bookseller believed detained by China was "involuntarily removed to the mainland" in its strongest comments yet on a case that has rocked the city.
The disappearance of Lee Bo, who holds a British passport and publishes books critical of Chinese politics, was a "serious breach" of an agreement signed with Beijing before the city was handed back to China in 1997, said foreign secretary Philip Hammond in a new report.
Four other booksellers from the Mighty Current publishing house also disappeared in October and the Chinese authorities have confirmed they are now under criminal investigation.
There are still question marks over what has happened to Lee, 65, the only publisher to have disappeared from Hong Kong.
Letters purportedly written by Lee and sent to his wife confirmed he was now on the mainland and said he had gone to China of his own volition to help with unspecified investigations.
Lawmakers and activists have accused Chinese authorities of snatching Lee from Hong Kong, contravening the semi-autonomous city's laws which do not allow Chinese police to operate within the territory.
"The full facts of the case remain unclear, but our current information indicates that Mr Lee was involuntarily removed to the mainland without any due process under Hong Kong SAR law," said Hammond in a regular six-monthly report on Hong Kong to the UK parliament.
"This constitutes a serious breach of the Sino-British Joint Declaration on Hong Kong and undermines the principle of 'One Country, Two Systems' which assures Hong Kong residents of the protection of the Hong Kong legal system," said Hammond.
Hong Kong's security bureau said it had no immediate comment.
The city enjoys freedoms unseen on the mainland, protected for 50 years under the joint agreement.
But there are growing fears those freedoms are being eroded as Chinese influence grows.
Booksellers Lui Por, Cheung Chi-ping and Lam Wing-kee disappeared in southern mainland China in October.
A fourth missing member of the company, Gui Minhai, a Swedish national, was paraded weeping on Chinese state television in January, where he said he had turned himself in for a fatal driving accident 11 years ago.
Gui had failed to return to Hong Kong from a holiday in Thailand in October.