Britain's "interventions" in Hong Kong have "seriously poisoned the atmosphere" of relations with China, Beijing's ambassador in London warned Thursday.

Liu Xiaoming also accused Western powers and media of spreading "the lies of the century" in their reporting of the treatment of Uighur Muslims in China.

"China has done nothing to weaken the mutual trust, we see the UK as a partner, a friendly country, we want to advance this golden era", Liu said in an online press conference.

"But unfortunately it's the UK side which has done things to undermine the trust," he added.

Britain's actions over Hong Kong and criticism of China's treatment of the Uighur population as "egregious human rights abuses" had "seriously poisoned" the relationship, he said.

The two countries have clashed over a new security law in Hong Kong, with Prime Minister Boris Johnson offering visas to millions of the city's residents.

Britain's last colonial governor of Hong Kong accused Beijing on Thursday of carrying out "an outrageous political purge" of pro-democracy parties there after a dozen candidates were disqualified for standing in an upcoming election.

As part of the 1997 handover of Hong Kong from Britain, China agreed to guarantee Hong Kong certain freedoms -- as well as judicial and legislative autonomy -- for 50 years in a deal known as "One Country, Two Systems".

Britain and China have also fallen out over the role of Chinese tech firm Huawei in building Britain's 5G network, with UK Prime Minister Boris Johnson announcing earlier this month that its involvement would be phased out over security concerns.

The ambassador claimed that Donald Trump was targeting China due to the upcoming election, and that the US president wanted a new Cold War.

"We have no interest in any Cold War," he said.

Liu was forced to answer questions over video footage that apparently showed Uighurs being loaded onto trains, during a recent BBC interview.

Rights groups and experts estimate that more than one million ethnic Uighurs and other Turkic-speaking minorities have been rounded up into a network of internment camps.

But Liu disputed the figure as "absurd" and claimed the video showed prisoners being moved by train.

"We hope the British media will disregard their arrogance and prejudice" and report in an "objective and fair manner" over the issue, he said.

He said claims of harsh detention camps were untrue, and compared the centres to similar de-radicalisation programmes in Britain and France.

However, he said China was opposed to a "so-called" independent investigation, saying it would be used for political purposes.