The government has narrowly defeated a move requiring the government to reconsider any trade deal with a country found by the high court to be committing genocide. The measure, backed by religious groups and a powerful cross-party alliance of MPs, was defeated by 319 to 308. The move giving the domestic courts a new role in determining genocide had been heavily endorsed by the Lords, and now peers will be asked by campaigners to reinsert the measure in a revised form back into the trade bill so forcing MPs to consider the proposal again. A US state department’s declaration that the treatment of the Uighur Muslims represents genocide and crimes against humanity, issued on Tuesday in the midst of the Commons debate, may embolden peers. The outgoing US secretary of state, Mike Pompeo, called for all appropriate multilateral and relevant judicial bodies to join the US in seeking to hold accountable those responsible for the atrocities. “I believe this genocide is ongoing, and that we are witnessing the systematic attempt to destroy Uighurs by the Chinese party-state,” Pompeo said in a statement. Greg Hands, the trade minister, opposed the amendment as a fundamental denial of parliamentary supremacy. He said he was open to holding further discussions with his rebel MPs, but offered no specific concession. A second measure, also endorsed by the Lords, requiring ministers to make a formal assessment of a country’s human rights record before striking a trade deal was heavily defeated by 364 to 267. The genocide amendment was devised by the independent peer Lord Alton as an attempt to break the current impasse whereby the international courts often cannot make rulings on genocide since nation states such as China do not recognise the relevant courts, or veto any reference to such issues. Alton had proposed the UK high court be able to make a preliminary determination that the government would then have to consider. The measure is primarily directed at protecting the Uighur Muslims in Xinjiang province, but a similar reference to the high court could be sought by any group claiming they are victims of genocide such as the Rohingya Muslims. The amendment had the backing of the Conservative Muslim Forum, the British Board of Jewish Deputies, the International Bar Association and a large array of Christian groups. Hands told MPs: “To accept this specific amendment would allow the high court to frustrate, even revoke trade agreements entered into by the government and approved after parliamentary scrutiny. This is a completely unprecedented and unacceptable erosion of the royal prerogative and not something the government could support.” He added the government had no plan to sign a free trade deal with China. In his only hint at a concession, he said the government was committed to make sure the expertise in the Commons on human rights is used and to explore how this could happen. He was backed by the former attorney general Sir Jeremy Wright who said it was not clear who the respondent would be in the event of a genocide case being brought in the high court. But he added the government did need to give MPs a greater say over future trade deals. Nus Ghani, a leading member of the inter-parliamentary alliance on China, said: “When the British Board of Deputies of Jewish colleagues state they are reminded of the Holocaust when they consider the state of the Uighur people it cannot get any worse than that.” Tom Tugendhat, the chair of the foreign affairs select committee, said the “vote was not about whether the courts or parliament decide on genocide. It’s already the courts who decide. The question is whose courts. The international courts are blocked, so this a way for the British people to take back control of our laws and our conscience.” Tobias Ellwood, the chair of the defence select committee, said: “The UK was suffering from an absence of clarity about what we believe in,” adding China was on a geopolitical collision course with the west. “The world watched and hesitated when genocide took place in Rwanda and indeed in Syria. Let’s not hesitate again.” Responding to the defeat Alton, the co-sponsor of the amendment in the Lords, said: “The fight does not end here. We will continue to do all we can to ensure that Uighurs and other victims of alleged genocide have a route to justice through UK courts.” He said the revised amendment would seek to “meet the perfectly reasonable argument that, once the court has reached a determination of genocide, parliament should then be able to vote on the revocation of a trade deal with the country concerned”.Helena Kennedy, the Labour peer and human rights lawyer, said: “I know that colleagues across all parties will not accept the loopholes in our existing systems which allow perpetrators of genocide to escape with impunity. The work to bring an improved amendment to the House of Lords begins immediately.”