The Chinese ambassador in London has been summoned to the Foreign Office to answer questions about the execution of a British man in China for drug smuggling.
Akmal Shaikh, 53, who had been convicted for smuggling 4kg of heroin, was executed by lethal injection on Tuesday.
His family and the British government had appealed for clemency, arguing the former businessman suffered from bipolar disorder and displayed extreme and erratic behaviour, the BBC reports.
Foreign Office Minister Ivan Lewis said he told the ambassador China had failed in its basic human rights responsibilities.
In a statement, the Chinese Embassy said Mr Shaikh had no previous medical record of mental illness.
It said the amount of heroin he had brought into China was enough to cause 26,800 deaths.
British Prime Minister Gordon Brown has condemned the execution in the strongest terms, saying he is appalled and disappointed that his government's persistent requests for clemency were not granted.
Mr Brown says he is particularly concerned that no mental health assessment was undertaken.
Claims Briton duped by smugglers
Akmal Shaikh's relatives said he had no knowledge of drugs found in his suitcase when he arrived in China two years ago, the BBC reports.
Chinese police had said they found 4kg of heroin in his luggage in the north-western city of Urumqi in 2007.
He maintained he had been tricked, and the suitcase did not belong to him. His daughter Leilla Hornsell told the BBC her father was duped by a drug smuggling gang.
The prisoners' rights charity Reprieve said Akmal Shaikh was the first European to be put to death in China since 1951.