The British foreign secretary, Philip Hammond, has said Beijing would be guilty of an “egregious breach” of Hong Kong’s autonomy if speculation that Chinese security forces had abducted a British bookseller in the former colony was confirmed.

Lee Bo, a 65-year-old British passport-holder, disappeared in Hong Kong last Wednesday and is one of five booksellers to have vanished from the region since October.

The whereabouts of the men – who specialised in books critical of China’s Communist party rulers – remains a mystery, with Beijing still refusing to directly comment on the scandal.

But the booksellers – who include a Swedish publisher, Gui Minhai, and three more junior bookshop staff – are widely suspected to have been detained by mainland security officials. Hong Kong police say they are investigating Lee’s disappearance.

Speaking on Wednesday in Beijing, where he is on a two-day visit, Hammond admitted that British officials not made any progress in ascertaining what had happened to Lee.

“There are obviously various strands of speculation about what might have happened to him but as far as I am aware they are all pure speculation at the moment. There is no hard information available,” the foreign secretary said after meeting with Yang Jiechi, China’s top diplomat.

However, Hammond voiced concern that Lee’s possible removal to the mainland would represent a major blow to the “one country, two systems” formula under which Hong Kong has operated with partial autonomy from Beijing since its return to China in 1997. Those rules outlaw mainland police from operating in Hong Kong and give Hong Kong judicial independence from authoritarian China.

Hammond said: “Just responding to the speculation that we’ve seen, it would not be acceptable for somebody to be spirited out of Hong Kong in order to face charges in a different jurisdiction. It is an essential part of the settlement in Hong Kong that it has its own judicial system and it is solely responsible for trying offences that occur in Hong Kong.”

Despite those concerns, the foreign secretary played down claims that the suspected abduction by Chinese security forces would spell doom for the ‘one country, two systems’ principle, as a number of prominent figures in Hong Kong have claimed.

Anson Chan, Hong Kong’s top civil servant at the time of handover, told the BBC: “If the abduction is proven true then I think you are spelling the death knell for ‘one country, two systems’. You can forget about it. Nobody would feel safe in Hong Kong.”

Hammond said: “We need to know what has happened and who is responsible for it, both ultimately responsible and proximately responsible. [These are] not necessarily the same thing, of course.



“But even in the worst case scenario that is being speculated, it seems to me that it would be quite an extreme step to say that because of what would be an egregious breach of the principle of ‘one country, two systems’ and the basic law and the Sino-British Joint Declaration... the whole thing had collapsed.”

Pro-democracy activists delivered a petition to the British consulate in Hong Kong on Wednesday, urging UK authorities to pressure China for answers over the missing booksellers. They also demonstrated outside the Chinese government headquarters in Hong Kong, accusing Beijing of kidnapping the booksellers because they had dared to publish politically sensitive books.

“China thinks that it’s just a matter for China,” Joshua Wong, the prominent student leader, told Hong Kong broadcaster RTHK. “But I would like to say it’s a matter for all citizens worldwide.”

Speaking alongside Hammond on Tuesday evening, the Chinese foreign minister, Wang Yi, appeared for the first time to confirm his government’s involvement in Lee’s disappearance.

He described the missing bookseller as being “first and foremost a Chinese citizen” but refused to confirm whether China had, in fact, detained the five men. “It is not necessary for anyone to make groundless speculations,” Wang said.

The disappearances, two of which took place outside mainland China, in Hong Kong and Thailand, have stirred fears about what many see as Beijing’s growing willingness to pursue its opponents beyond its own borders.

Asked if he could guarantee that the UK-based relatives of Lee Bo and Gui Minhai would not also disappear, Hammond said: “Certainly in the UK everybody should feel safe from being spirited anywhere. I would have a high degree of confidence that people in the UK are safe from any such activity.”