This blueprint would be elaborated on in the Hong Kong Basic Law (the post-handover regional constitution) and the central government's policies for the territory were to remain unchanged for a period of 50 years after 1997.

However, as Germany, Japan, and Russia coerced China into granting concessions in the late 1890s, Britain considered another expansion of Hong Kong to bolster the colony's defence against attack from these other great powers.

[2] When France obtained a lease for Guangzhouwan, only 210 miles (340 km) away from Hong Kong,[3] Britain entered into negotiations with the Qing to acquire the New Territories as a compensatory concession in 1898.

Alternate plans that involved offering China a substantial loan and settling land disputes on the Burmese border were suggested, but these ideas similarly did not progress past discussion.

[7][8] In the immediate post-war period, the Nationalist government continued this dialogue with the British about the future of Hong Kong, which included discussions of a full retrocession and proposals of turning the colony into an international city.

The Chinese were content with the political status of the colony for the time being so long as no efforts were made to introduce democratic development in the territory; they were simply hostile to the idea of a potentially independent Hong Kong.

The United Kingdom did not raise any objections to this and the local population did not think the move was significant, but the implication of this change was that Communist China alone would determine the territory's future, excluding the people of Hong Kong.

[14] However, the disturbances never gained local support and the subsequent restoration of public order conversely resulted in the colonial government achieving increased popularity among the territory's residents.

Deng rejected this suggestion, but he informed the governor that while sovereignty over Hong Kong belonged to China, the territory held a special status that would continue to be respected.

Market reaction was optimistic; stock valuations rose and further investment in real estate boosted the value of Hong Kong's land to the highest in the world.

[26] Formal negotiations began in September 1982 with the arrival of British Prime Minister Margaret Thatcher and Hong Kong Governor Edward Youde in Beijing to meet with Chinese Premier Zhao Ziyang and paramount leader Deng Xiaoping.

[31] Although the UK had just successfully defended its hold on the Falkland Islands in a war against Argentina, Hong Kong's proximity to mainland China made a military defence of the territory impossible.

[30][37] Even if the two sides had agreed on the binding nature of the Treaty of Nanking and Convention of Peking, the vast majority of the colony's land still would have reverted to China at the conclusion of the New Territories lease.

[40] Early in the process, British officials had used the analogy of a "three-legged stool" to describe a scenario where Hong Kong was party to the negotiations with the United Kingdom and China.

[42] The Foreign Office rejected holding a general referendum on the future of the colony due to vehement opposition from the Chinese[43] and because it assumed that educating the public on the complexity of the issue would be too difficult.

[44] Although the Unofficial Members of the Executive and Legislative Councils had repeatedly petitioned the British negotiators to insist on continued administration for as long as possible, they were ultimately unsuccessful.

[49] The Chinese initially wanted the Joint Liaison Group to act as an oversight committee during the transition period of administering Hong Kong up to the handover date.

This was completed in three months,[52] and on 26 September 1984, a draft copy of the Joint Declaration was initialed by British Ambassador to China Richard Evans and Chinese Vice Foreign Minister Zhou Nan.

[53] The final version was signed on 19 December 1984 by Prime Minister Thatcher and Premier Zhao in the Great Hall of the People in Beijing;[54] the treaty came into force when instruments of ratification were exchanged on 27 May 1985[55] and was registered at the United Nations by both governments on 12 June 1985.

[61] During the transition period from the date the treaty came into force until 30 June 1997, the United Kingdom would continue to be responsible for administering Hong Kong with the objective of maintaining its economic prosperity and social stability.

Socialism as practised in mainland China would not be extended to Hong Kong and the territory's capitalist economy and the civil liberties of its residents (such as freedom of speech, assembly, and religion) would be protected and remain unchanged for 50 years.

In the first half of this period, it would consider actions necessary to maintain Hong Kong's status as a separate customs territory and ensure continuity of its international rights and obligations.

[73] During the second half leading up to the handover, the Liaison Group would consider actions needed to ensure a successful transition in 1997 and assist the incoming regional government in developing relations and agreements with other countries and international organisations for economic and cultural purposes.

[83] The signing of the Joint Declaration caused some controversy in the United Kingdom because UK's Conservative Party Prime Minister Margaret Thatcher was agreeing with China's Communist government represented by Deng Xiaoping.

Although discussions on the future of Hong Kong had started in the late 1970s, the final timing of the Joint Declaration was more affected by property and economic factors rather than geopolitical necessities.

For example, in 1999 the government of the HKSAR asked China's State Council to seek an interpretation by the National People's Congress Standing Committee on a provision in the Basic Law.

[99] The Foreign Office has labelled the Causeway Bay Books disappearances in 2015,[100] enactment of the Hong Kong national security law in 2020,[101] disqualification of opposition Legislative Council candidates in 2020,[102] and electoral reform in 2021 as serious breaches of the treaty.

[104] China disregards accusations of Joint Declaration breaches as foreign interference and neocolonist tampering,[105][106] and considers Hong Kong matters to be part of its internal affairs.

The list of sanctioned persons includes Chief Executive Carrie Lam, principal officials of the Hong Kong government, and members of the Standing Committee of the National People's Congress.

[116][117] In March 2024 the pro-Beijing legislature in Hong Kong fast-tracked Article 23, a new security law which introduces harsh new penalties such as life imprisonment for new offences such as external interference and insurrection.