Britain said on Wednesday that proposed changes to Hong Kong's electoral system would be another attack on the freedoms of its former colony, and that the government had raised its concerns directly with Beijing.
"Such measures, if introduced, would be a further attack on Hong Kong's rights and freedoms," Foreign Office minister Nigel Adams told lawmakers. "The Chinese and Hong Kong authorities can be in no doubt about the seriousness of our concerns."
China's rubber-stamp parliament, the National People's Congress (NPC), is expected on Thursday to approve a resolution that will reduce democratic representation in Hong Kong institutions and vet any candidates for "patriotism".
Adams said Britain would wait to see what the actual changes were before making its final assessment.
He said he could not speculate on Magnitsky-style sanctions against individuals over China's actions in Hong Kong, but said that such measures remain under very close review.
Britain has previously said it is considering Magnitsky sanctions because it judges that Beijing has broken the terms of the 1997 handover of Hong Kong to China.
Hong Kong returned to Chinese rule with the promise of wide-ranging autonomy and freedoms that pro-democracy activists, who brought parts of the city to frequent halts in sometimes violent protests in 2019, say are being whittled away by Communist Party rulers in Beijing. China denies the accusation.