In Hong Kong, China’s efforts to assert control over the semiautonomous territory have provoked weeks of angry protests. And in Britain, the government is in turmoil over plans to exit the European Union in a way that could deflate the economy.

The Hong Kong offer would require Britain to cede a corporate crown jewel — one whose roots trace back to 1571 — at a time when London’s centuries-long status as a leading financial capital is already in doubt because of Brexit.

Britain has been more open to investment from China and Hong Kong than other Western countries have. Li Ka-shing, the Hong Kong tycoon, has invested in British infrastructure for years, and London has been slow to bend to Washington’s pressure not to use equipment from Huawei, the Chinese maker of telecom gear. But the Hong Kong protests have brought questions of Chinese influence to the fore.

The Chinese government is the largest shareholder of the Hong Kong exchange, with the right to name six of its 13 board members, and Beijing’s responses to the antigovernment demonstrations in Hong Kong are likely to lead British officials to closely scrutinize the deal for any signs of Chinese government influence. Britain’s business minister, Andrea Leadsom, said in a Bloomberg Television interview on Wednesday that regulators would “look very carefully at anything that had security implications for the U.K.”

Previous foreign takeovers of British companies have been derailed or delayed on similar grounds, such as a proposed takeover last year of Northern Aerospace by a Chinese rival. The British government announced plans last year to significantly toughen its scrutiny of foreign takeovers, with a particular eye on those coming from China.