Former prime minister Liz Truss has made a personal plea for Rishi Sunak to brand China as a "threat" to UK security during a visit to Taiwan.
The ex-prime minister challenged Mr Sunak to deliver on pledges he made last summer to clamp down on China.
Ms Truss made the speech in Taipei City on Wednesday, making her the first former prime minister to visit Taiwan since Margaret Thatcher.
The Chinese Embassy called Ms Truss's visit "a dangerous political stunt".
It added that the visit "will do nothing but harm to the UK".
In the speech, Ms Truss urged the West not to work with China, warning that totalitarian regimes "don't tell the truth".
She drew comparisons between the tensions between China and Taiwan, and the Russian invasion of Ukraine.
During the Conservative party leadership contest, Ms Truss pledged to take a firm stance against the Chinese government, and wanted to declare China under Communist Party rule a "threat" to national security.
But after her short-lived time in No 10, her plans were never realised.
Her successor Rishi Sunak, also declared China as "the biggest-long term threat to Britain", and promised to close all 30 of Beijing's Confucius Institutes in the UK.
Confucius Institutes, which teach Chinese language and culture, came under fire after critics and charities accused the centres of being used by the Chinese government to spread propaganda under the guise of teaching, interfere with free speech on campuses, and even spy on students.
While Mr Sunak has not closed the institutes, the UK government is expected to promise that it will stop funding Mandarin teaching at the centres.
In her speech, Ms Truss said Mr Sunak was "right" to make those pledges. "We need to see those policies enacted urgently," she added.
The prime minister updated the UK's integrated review on foreign and defence policy in March to describe China as representing an "epoch-defining and systemic challenge".
In her speech, Ms Truss said the review needed to be amended to "state clearly that China is a threat".
She called on the UK government to support Taiwan joining the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP) trade agreement - and for it to block China from joining.
The former prime minister also called for the development of "an economic Nato", which "supports freedom and proper free enterprise".
She suggested countries including the G7 nations, members of the EU, South Korea and Australia could join this kind of group.
Ms Truss said: "We cannot rely now on the UN security council, which was recently chaired by Putin's Russia.
"We cannot rely on the World Trade Organisation to make sure fair trade rules are in place. That's why we need other alternatives to get things done."
Ms Truss made the speech at the invitation of the Prospect Foundation, a think tank. It forms part of the former UK leader's five-day visit to the country.
Last week, senior Conservative MP Alicia Kearns accused former Prime Minister Liz Truss of "Instagram diplomacy" over her planned visit to Taiwan.
Ms Kearns, who chairs the Commons Foreign Affairs committee, told the Guardian the trip was "performative, not substantive".
But Ms Truss accused her Tory colleague of "misusing" her position "to engage in petty political attacks", and said her visit aimed to show "solidarity" with Taiwan.
Taiwan and China split in 1949 following a civil war that ended with the Communist Party in control of the mainland. China views Taiwan as Chinese territory.
Source: BBC