China yesterday executed a Briton caught smuggling heroin, prompting a British outcry over what it said was the lack of any mental health assessment.
Beijing called the British criticism groundless interference in its judicial sovereignty.
Relatives of Akmal Shaikh, 53, and the British government had appealed for clemency, arguing the former businessman suffered from bipolar disorder, or manic depression.
China's Supreme Court rejected the appeal, saying there was insufficient evidence of mental illness.
Mr Shaikh was the first European citizen executed in China since 1951, Western rights groups say.
British Prime Minister Gordon Brown condemned the execution, carried out in Urumqi, capital of the far-west region of Xinjiang, saying he was "appalled and disappointed that our persistent requests for clemency have not been granted.
"I am particularly concerned that no mental health assessment was undertaken," he said in a statement.
British Foreign Office Minister Ivan Lewis summoned China's ambassador in London, Fu Ying, to protest at the execution.
"I made clear that the execution of Mr Shaikh was totally unacceptable and that China had failed in its basic human rights responsibilities in this case...," Mr Lewis said in a statement after what he described as a "difficult conversation".
China rejected the British criticism.
"Nobody has the right to speak ill of China's judicial sovereignty," Chinese Foreign Ministry mouthpiece Jiang Yu said. "We express our strong dissatisfaction and resolute opposition over the groundless British accusations."
Mr Shaikh was executed by injection, China's official Xinhua news agency reported. His family said it was "stunned and disappointed" and criticised China's stance on his mental health.
The European Union and France both condemned the execution.
The 27-nation EU's presidency said it deeply regretted that China had not heeded repeated calls from the EU and Britain for Mr Shaikh to be spared the death penalty.
Mr Shaikh's defenders, including British rights group Reprieve, which lobbies against the death penalty, say he was duped into smuggling heroin by a gang who promised to make him a pop star.
Arrested in 2007, Mr Shaikh, a Muslim, had had his last appeal rejected by a Chinese court on December 21. Reprieve posted on the Internet a recording Shaikh made of a song, Come Little Rabbit, which it said he believed would be an international hit and help bring about world peace.
Human rights group Amnesty International said Mr Shaikh's execution "highlights the injustice and inhumanity of the death penalty, particularly as it is implemented in China".
Mr Lewis told BBC radio the execution made him feel "sick to the stomach", but said Britain "must and will continue to engage with China".
China executes more people than any other country, with about 1,718 executions in 2008, far surpassing Iran at 346 and the United States at 111, according to Amnesty International. China does not release an official count of its executions.
The case could increase Chinese resentment over what Beijing often calls "interference" in its internal affairs, mindful of humiliating defeats by Britain during the Opium Wars of the 1800s.
"We hope that the British side can view this matter rationally, and not create new obstacles in bilateral relations," Ms Jiang said.
Britain is China's third-largest trade partner in Europe, with total trade of $45 billion in 2008.
British economic ties with China have strengthened under Mr Brown, although the two nations recently criticised one another over the troubled Copenhagen climate change negotiations.