The British government should have done more to support Hong Kong's efforts for democracy, MPs have said in a highly critical report.
The Commons Foreign Affairs Select Committe rebuked ministers for their "mild" response to China's decision to block a fact-finding mission to the former British colony.
The committee added it was "profoundly disappointed that the Foreign Office did not summon the Chinese ambassador after the move.
China said the planned visit - due to take place amid mass pro-democracy protests - would have been an unwanted intrusion on internal affairs.
Sir Richard Ottaway, chair of the committee, said the move was part of a "troubling pattern" during which Hong Kong's moves toward free elections - promised in the Sino-British declaration of 1984 - appeared to be undermined by Beijing.
"We are concerned that the FCO's lack of clarity in expressing its views on political and constitutional developments in Hong Kong may be damaging the UK's reputation there," he said.
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Hong Kong celebrated the new year with a hi-tech light and firework display set to music over the city's waterfront.
Hong Kong authorities have started to clear the main pro-democracy protest site that has choked the Chinese-controlled city for more than two months, moving to stamp out street demonstrations that have demanded free elections.
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Hundreds of police swept into the Admiralty site next to government offices and the main Central business district early on Thursday to enforce an injunction to clear barricades erected by protesters.
Student groups have occupied some of the Asia financial centre's most important arteries since late September, creating havoc for commuters and frustrating residents through a largely peaceful demonstration dubbed the "Umbrella Movement".
Hong Kong police received the green light to clear the sites on Tuesday after a bus company was granted an injunction by the city's High Court against street blockades at the site in Admiralty.
David Cameron believes the Chinese authorities' decision to ban a British parliamentary committee from entering Hong Kong is "mistaken" and "counter-productive".
The Prime Minister's spokesman told reporters at a regular briefing:
The Prime Minister's view is that the decision with regard to the Foreign Affairs Select Committee is a mistaken one.
The reason why the Prime Minister thinks it is a mistaken decision is because it is counter-productive. It only serves to amplify concerns about the situation in Hong Kong, rather than diminishing concerns.
The head of a parliamentary committee banned from entering Hong Kong has told ITV News the actions of the Chinese government are "a very worrying development".
MPs are pressing for an emergency Commons debate after China said it would not let the Foreign Affairs Committee enter the former British colony.
The committee had been planning the visit as part of an inquiry into relations with the UK 30 years after the joint declaration which led to the handover of Hong Kong to China in 1997.
The Chinese government has claimed the trip would be a "highly inappropriate act which constitutes interference in China's internal affairs".
Committee chair Sir Richard Ottaway said: "For them to be banning a parliamentary committee from one of their G20 partners from visiting Hong Kong I think is a very worrying development about the direction of travel of China."
Pro-democracy protesters have clashed with riot police outside the headquarters of Hong Kong's government, with 18 people arrested.
Government offices and shops were forced to temporarily close while the stand-off continued.
Police charged the protesters with batons and pepper spray as they defied orders to retreat.
The demonstrators are angry at the Chinese government in Beijing for refusing to allow greater independence and democracy in the former British colony.
Thousands of pro-democracy activists forced the temporary closure of the Hong Kong government's headquarters today after they clashed with police outside.
Chaos erupted as commuters made their way to work, with hundreds of protesters surrounding Admiralty Centre, which houses offices and retail outlets, in a tense stand-off with police.
The central government offices and the legislature were forced to close in the morning, as were scores of shops.
The latest flare-up, during which police charged protesters with batons and pepper spray, marked an escalation in the civil disobedience movement.
British lawmakers will not be allowed to enter Hong Kong as part of an inquiry into Britain's relations with its former colony and progress towards democracy there, the head of a parliamentary committee said.
"I have been informed by the Chinese Embassy that if we attempt to travel to Hong Kong we will be refused entry," foreign affairs select committee chairman Richard Ottaway said in a statement.
The committee is looking at Britain's relations with Hong Kong 30 years after it agreed terms for handing the city over to China.
The news comes as thousands of pro-democracy activists in Hong Kong have clashed with police over the way the city's next leaders will be elected in 2017.