LOND ON/URUMQI, China, (AFP/Reuters) - British Prime Minister Gordon Brown said he was appalled at Chinas execution of a Briton caught smuggling heroin on Tuesday, prompting China to denounce British accusations and defend its court system. Relatives of Akmal Shaikh, 53, the British government and the European Union had appealed for clemency, arguing the former businessman suffered from bipolar disorder, or manic depression. Chinas Supreme Court rejected the appeal, saying there was insufficient evidence of mental illness. Brown condemned the execution, carried out in the far-west region of Xinjiang, in strong words that may raise diplomatic temperatures over the case. I condemn the execution of Akmal Shaikh in the strongest terms, and am appalled and disappointed that our persistent requests for clemency have not been granted, he said in a statement issued by the Foreign Office. I am particularly concerned that no mental health assessment was undertaken. The European Union echoed the British Prime Ministers words. It deeply regrets the fact that China has not heeded the repeated calls by the European Union and one of its member states for the death sentence passed against Mr Shaikh to be commuted, the presidency of the 27-nation bloc said in a statement. China was just as determined in its defence of the execution. Nobody has the right to speak ill of Chinas judicial sovereignty, Chinese Foreign Ministry spokeswoman Jiang Yu said. We express our strong dissatisfaction and resolute opposition over the groundless British accusations. Shaikh was executed by injection, Chinas official Xinhua news agency reported. His family said it was stunned and disappointed and criticised Chinas stance on his mental health. We are astonished at suggestions that Akmal himself should have provided evidence of his own fragile state of mind, they said in a statement. Shaikh was the first European citizen to be executed in China since 1951, Western rights groups say. Akmal Shaikhs 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. Meanwhile, Britain summoned Chinas Ambassador to the Foreign Office to protest the totally unacceptable execution of Akmal despite repeated appeals for clemency, a minister said. I had a difficult conversation with the Chinese ambassador today, said Junior Foreign Minister Ivan Lewis after the meeting on the execution of Akmal Shaikh, who was said to have suffered from a mental illness. I made clear that the execution of (Akmal) Shaikh was totally unacceptable and that China had failed in its basic human rights responsibilities in this case, in particular that Chinas court had not considered the representations made about Akmals mental condition.