Prime Minister David Cameron has warned China it is "mistaken" and "counter-productive" to bar a British parliamentary fact-finding mission from Hong Kong.
Beijing said it would not allow MPs from the House of Commons Foreign Affairs Select Committee to enter the former British colony, where pro-democracy demonstrators have been staging protests since September.
The situation was described as "extremely serious" by Commons Speaker John Bercow and Downing Street said that the action had "amplified" concerns about the situation in Hong Kong, which has enjoyed a degree of autonomy from Beijing under the "one country, two systems" arrangements instituted at the time of its handover from UK control in 1997.
Mr Bercow granted a rare emergency debate on the issue in the Commons tomorrow after an application from the committee's chairman Sir Richard Ottaway.
The committee has postponed its trip to Hong Kong, but will continue to take evidence - potentially by videolink.
Sir Richard said "We are not going to be pressured by the Chinese government into abandoning our inquiry, nor are we going to cancel plans to hear from people in Hong Kong.
"The approach taken by China has been very revealing, and we shall be looking carefully at how the Foreign Office responds."
Granting the urgent debate, Mr Bercow said: " This is an extremely serious matter for which I can confess I can think of no exactly comparable precedent in my 17-and-a-half years in the House."
Meanwhile, Business Secretary Vince Cable said that the Government would urgently look again at whether exports of tear gas from the UK to Hong Kong should be blocked in response to concerns raised about the continued use of the crowd control weapon.
Mr Cameron's official spokesman told a regular Westminster media briefing: "The Prime Minister's view is that the decision with regard to the Foreign Affairs Select Committee is a mistaken one.
"We will continue to have a dialogue with the Chinese authorities on this, both through the Foreign Office here in London with the Chinese Embassy in London and through our embassy in Beijing.
"The argument that we will be taking forward with the Chinese authorities is that 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."
Foreign Office minister Hugo Swire expressed Britain's concern to Chinese vice-minister for international affairs Guo Yezhou.
The pair spoke in a long-scheduled meeting at the Foreign Office in Whitehall during a visit to the UK by Mr Guo.
As a co-signatory to the 1984 joint declaration which underpinned the handover of sovereignty over Hong Kong to China, the UK has "a legitimate concern" in the implementation of its terms, said the spokesman.
As part of this, it was "understandable" that MPs from the parliamentary committee should want to visit the territory - as they have done on previous occasions - to scrutinise how the terms are being implemented.
Committee chairman Sir Richard Ottaway said they had been told by the Chinese embassy that they would be turned back if they tried to enter Hong Kong, which they had been planning to visit as part of an inquiry into its relations with the UK 30 years after the joint declaration.
But the probe has raised hackles in Beijing, with the committee's Chinese counterpart condemning it as a ''highly inappropriate act which constitutes interference in China's internal affairs''.
The Foreign Office (FCO) said the decision to deny the MPs access to Hong Kong was "regrettable" and that it had made its view known to the Chinese authorities at "the most senior levels".
The move comes as police in Hong Kong arrested 40 pro-democracy demonstrators in the latest clashes between the authorities and the protest movement which began in late September.