After two years of negotiations, UK Prime Minister Margaret Thatcher and China’s Premier of the State Council Zhao Ziyang signed the Sino-British Joint Declaration. Under the agreement, Britain would relinquish control of the New Territories to China following the end of the 99-year lease (July 1, 1997). Britain would also relinquish control of Hong Kong Island and the southern part of the Kowloon Peninsula. China declared that following the return to China in 1997, Hong Kong would become a Special Administrative Region and retain a high degree of autonomy under the ‘One country, two systems’ principle. The intertwining of the Guangdong and HK economies accelerated after the 1984 agreement.