Video report by ITV News Asia Correspondent Debi Edward
Jeremy Hunt has warned Beijing to stick to a "legally-binding" agreement to preserve freedoms in Hong Kong.
But he also said there is “no reason” why Britain cannot continue to have good relations with China, despite an escalation of the dispute over Hong Kong.
The Foreign Secretary refused to outline what sanctions he could impose on China, after the country’s ambassador in London was summoned for a dressing down from the UK’s top diplomat.
The Foreign Office and Beijing have been involved in a spat following a call from Mr Hunt not to use the protests in Hong Kong as a “pretext for repression”.
Asked on Friday what form sanctions might take, Mr Hunt would not be drawn on specifics.
"No foreign secretary would ever spell out what any consequences might be because that actually might provoke the very thing we are trying to avoid," he said.
"But I do want to send a message that we would not let it rest and it would be a very serious matter for us if that agreement were to be breached."
But Mr Hunt went on: "As Foreign Secretary, I have taken a lot of steps to nurture good relations with China but sometimes you have to say tough things to friends and we have an internationally, legally-binding agreement with China over the future of Hong Kong.
"I want to send the message to China that we expect that agreement to be honoured in both letter and spirit."
China’s foreign ministry had earlier hit back and ambassador Liu Xiaoming lambasted the UK Government over its approach.
Mr Liu was then hauled in the Foreign Office in London to meet Sir Simon McDonald, the head of the diplomatic service, following the "unacceptable and inaccurate" comments from the ministry of foreign affairs in Beijing.
Geng Shuang, a spokesman for Beijing’s ministry of foreign affairs, said Mr Hunt “appeared to be “basking in the faded glory of British colonialism and obsessed with lecturing others”.
After ambassador Liu was summoned, an FCO spokesman said: “The FCO’s Permanent Under Secretary Sir Simon McDonald told the Chinese ambassador that the comments made on UK policy towards Hong Kong by the Chinese ministry of foreign affairs spokesperson were unacceptable and inaccurate.
“The British Government’s position has been set out clearly by the Foreign Secretary and other ministers.”
The turmoil in Hong Kong has seen protesters storm parliament and raise the old British colonial flag in the legislative chamber on the 22nd anniversary of the territory’s return to Chinese rule on July 1.
Police used tear gas against anti-government activists.
The scenes follow unrest in the former colony over a controversial extradition law.
Mr Liu used a press conference to warn that Britain had damaged its relationship with China by interfering in Hong Kong following unrest in the region.
In a reference to Mr Hunt, he said it was “very disappointing” when senior officials “of his calibre” show support for “law-breaking” people.
He urged the Government to reflect on the “consequences of its words and deeds” regarding the former British colony.
He said: “I think the relationship in a way has been damaged by the interference of the British Government in Hong Kong because, as I said, the fundamental principles guiding our two countries is mutual respect, non-interference into internal affairs.
“If the British Government go further it will cause further damages, so that is why I’m calling the British Government to reflect the consequences of its words and deeds with regards to Hong Kong.”