Thirty years ago this month, Britain and China signed the Sino-British Joint Declaration on the Question of Hong Kong, under which London agreed to restore Hong Kong to China in 1997 and Beijing spelled out its policy of "one country, two systems" for the then British colony, which would "enjoy a high degree of autonomy, except in foreign and defense affairs which are the responsibilities of the Central People's Government" for 50 years, that is, until 2047.

In July, the British Parliament's Foreign Affairs Committee announced that it would conduct an inquiry into the United Kingdom's relations with Hong Kong. According to the committee, the inquiry will consider how the British government monitors the implementation of the Joint Declaration, as well as the U.K.'s relations with Hong Kong, including economic and cultural ties.

Last week the committee ran into a brick wall. China told the committee its members would be denied visas for Hong Kong.