No one has told him that he is about to die. But unless last-minute pleas for his life prove successful, a Kentish Town taxi driver who suffers from mental illness will be shot dead by the Chinese authorities within 24 hours.

Akmal Shaikh, a 53-year-old father of five who has been accused of smuggling four kilos of heroin into China's western Xinjiang province in 2007, could become the first Briton to be executed in China in modern times, and the first EU national to face the death penalty there in 50 years. But he has not been informed that his execution by a bullet to the neck has been scheduled for 10.30 tomorrow morning. The Chinese government says the information is being withheld on "humanitarian grounds".

Mr Shaikh's friends and family say he suffers from bipolar disorder and was too ill to stand trial. His cousins Soohail and Nasir Shaikh have travelled to China to try and deliver pleas for mercy to President Hu Jintao. But so far those pleas have fallen on deaf ears.

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In his petition, his cousin Mr Soohail says: "We plead for his life, asking that a full mental health evaluation be conducted to assess the impact of his mental illness, and that recognition be made that he is not as culpable as those who might, under Chinese law, be eligible for the death penalty."

Clive Stafford Smith, the director of the human rights charity Reprieve, has petitioned for his pardon, amid fears that Beijing is aggrieved by the international reaction to its stance at the Copenhagen climate talks – in particular that of Britain, which blamed China for the failure of the talks when Ed Miliband said it had "hijacked" discussions.

"I like to think the Chinese will show compassion but I don't know," Mr Stafford Smith said yesterday. "I think on one level China is aggravated by what happened at Copenhagen, but I hope it won't hold that against him."

China executes more people than all other countries put together but rarely executes Westerners. The Foreign Office says it has pressed hard for his release. Over the last six months, the UK has forcibly raised the case with senior Chinese officials 10 times to no effect. Prime Minister Gordon Brown and the actor Stephen Fry are among many who have tried to intercede.

One of the key pieces of evidence in favour of the argument that Mr Shaikh is a sadly deluded figure, is a pop song he recorded called "Come Little Rabbit". Reprieve released the song in the hope that it would help convince the Chinese judiciary of his fragile mental state and halt his execution. Before he left for China, Mr Shaikh recorded the song, which he was convinced would bring peace to the world.

Among other possibly delusional moves, Mr Shaikh wrote emails to US and British officials calling himself a millionaire and a messiah. He moved to Poland several years ago, where he intended to set up an airline, which he was in no position to do. While in Warsaw, he wrote the song with a man named Carlos, who said he knew a producer in Kyrgyzstan who could help.

Mr Shaikh had no experience of singing in public before he headed to China, and campaigners say he was tricked into carrying the suitcase in Kyrgyzstan by the "producer", who was working for a criminal gang for whom he unwittingly carried drugs.

The UN special rapporteur on summary executions, Philip Alston, has condemned Beijing's stance. Insisting that there are "strong indications" Mr Shaikh suffers from mental illness, he called the prospective death penalty "a major step backwards for China".

Mr Shaikh's brother Akbar has written to the Chinese ambassador in London invoking the suffering of his mother. "She is a frail woman," he wrote, "and our family have not been able to break the news to her that she may lose her youngest child next week."

Working against Mr Shaikh are his insistence on holding his own defence, and his insistence during his trial that neither he nor his family have a history of mental illness. Witnesses say that his testimony was at times so absurd that even the judges were laughing.

The Chinese government says Mr Shaikh's conviction was carried out according to the country's laws. "Drug smuggling is a grave crime in international practice. During the entire process, the litigation rights and the relevant rights and interests of the defendant were fully respected and guaranteed. China has offered prompt consular information to the UK and arranged consular visits," said Foreign Ministry spokeswoman Jiang Yu.