Hong Kong (CNN) China has reacted angrily to a British report voicing concerns over Beijing influence on Hong Kong's legal affairs, demanding that London stop meddling in China's internal issues.

The report "contains willful comments on Hong Kong affairs," Chinese Foreign Ministry spokesman Geng Shuang said Thursday.

"We by no means accept the unwarranted accusations against China in some parts of the report."

Missing booksellers

He cited the case of five booksellers who disappeared in late 2015 , only to later reemerge in mainland China, including Lee Bo, who holds British citizenship.

One bookseller who returned to the city, Lam Wing-kee, told CNN how he was detained by "special forces" officers during a visit to mainland China and kept in solitary confinement for months.

"Lee's involuntary removal from Hong Kong to the mainland constituted a serious breach of the Sino-British Joint Declaration by undermining the 'one country, two systems' principle," Johnson said, referring to the system which grants Hong Kong limited autonomy and control of its own legal affairs.

The Chinese government is "confident and determined in carrying forward 'one country, two systems'," Geng said.

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'Stop meddling'

Britain should "stop meddling in Hong Kong affairs," Geng said, emphasizing that the city is a Chinese special administrative region.

Despite Beijing's complaints however, the UK does have a limited obligation to Hong Kong as a signatory to the 1984 Sino-British Joint Declaration , which transferred control of the city between the two countries.

Westminster issues regular twice yearly reports on the situation in Hong Kong, including democratic development in the city.

"A more democratic and accountable system of government ... (would) help strengthen those rights and freedoms, including academic freedom and freedom of expression, which have come under increasing pressure over the past two years," Johnson said.