British Prime Minister Boris Johnson is locked in a battle with parliament over the country's approach to trade with China, fuelled by criticism that his government is lagging its peers in its condemnation of the treatment of Uighur Muslims in Xinjiang.
The rights and wrongs of trading with China, the world's second-largest economy, have become a burning question for governments around the world. All eyes are on US President Joe Biden's new administration after it endorsed a Trump-era determination that genocide was being committed in Xinjiang.
In Britain, the dilemma of trying to balance moral concerns about Xinjiang with the economic reality that China is a vast and important market is playing out in a bitter row over trade legislation making its way through parliament.
Although Britain is not currently seeking a free trade deal with China, lawmakers in both houses of parliament want a way to stop the government signing deals with countries found to have committed genocide. They cite China as a prime example.
Beijing denies accusations of rights abuses in Xinjiang.
Britain has denounced the torture, forced labour and sterilisations that it says are taking place against Muslim Uighurs on an "industrial scale".
But the government says that it is for courts to make rulings on genocide, and that lawmakers should not create a system in which court rulings dictate trade policy or which allows the lines between the judiciary and parliament to become blurred.
Courts may also be too slow to reach a verdict and open to litigation designed to block trade, ministers have argued in defence of keeping the decisions separate.
The battle over procedure is hypothetical, unless Britain opens trade talks with Beijing.
But it is symbolic of a groundswell of opinion in parliament that Johnson should be doing more to put pressure on China over Xinjiang.
"We fail to predict genocide, we fail to prevent genocide, to protect victims of genocide and to prosecute perpetrators of genocide," David Alton, a lawmaker in parliament's upper chamber, said on Tuesday.
So far, ministers have succeeded in watering down proposals for oversight of trade deals with parties suspected of genocide - seeing off a proposal that could have resulted in domestic courts ordering a veto on deals. The government says such rulings would be time-consuming.
But parliament is still fighting, and rebellions have whittled away much of Johnson's large majority.
Johnson's authority on the issue will be tested when the latest proposal, passed on Tuesday by the unelected House of Lords against the government's wishes, is put before the elected House of Commons for approval.
The proposal gives a "Parliamentary Judicial Committee" - a new body made up of lawmakers who have served at the highest levels of the judiciary - the power to determine whether genocide was being committed by a potential trade partner.
If Johnson chooses to fight against the latest proposal he risks further criticism at a time when he is trying to recast post-Brexit Britain as a force for good on the international stage during its presidency of the G7 and hosting of a global climate conference.
The government has yet to set out its position on the Lords proposal. A spokesman for Johnson repeated the prime minister's "grave concerns" about the rights abuses in Xinjiang and his belief that courts should determine whether genocide has been committed.
The last time the issue came before parliament Johnson, whose party has a working majority of 87, won by only 15 votes as 31 of his own party rebelled and several abstained. The date for the next vote has not yet been set