Akmal Shaikh's family say he suffers from bipolar disorder
A Briton facing execution in China does not yet know he is to be killed later this week and will only find out 24 hours in advance, it has emerged.
Akmal Shaikh, 53, from London, is due to be executed on 29 December after he was convicted of smuggling heroin.
Legal charity Reprieve said the lack of notice "raises obvious concerns" and hopes the authorities "show clemency".
Mr Shaikh's supporters say he is mentally ill and Gordon Brown has asked Chinese authorities for clemency.
Two of his cousins, Soohail and Nasir Shaikh, are in China and plan to deliver a last-ditch plea for mercy on his behalf to President Hu Jintao.
British consular staff have also flown to the Chinese region of Xinjiang to see the condemned Briton and discuss his case with local officials.
CHINA DEATH PENALTY
China executed 1,718 people in 2008, according to Amnesty International
Last year 72% of the world's total executions took place in China, the charity estimates
It applies to 60 offences, including non-violent crimes such as tax fraud and embezzlement
Those sentenced to death are usually shot, but some provinces are introducing lethal injections
According to Reprieve, Chinese authorities have said knowledge of his execution is being withheld from the prisoner on "humanitarian grounds".
Clive Stafford Smith, the charity's director, said: "We hope that the Chinese authorities have kept him in the dark that his execution is only hours away because they are going to show clemency.
"Only then would it truly be humanitarian for him to be the only person in the world not allowed to know."
The man's relatives intend to deliver petitions seeking a legal review to China's Supreme People's Court and to the local court in the north-western city of Urumqi where Mr Shaikh was arrested in September 2007.
Reprieve said the men, who are brothers, also planned to appeal to China's president and to the Standing Committee of the National People's Congress, which is responsible for considering petitions for pardon or clemency.
Mr Shaikh has had no contact with his family for two years, but the cousins hope they may be granted a prison visit with him.
The Briton has denied all knowledge of the 4kg of heroin found in his possession.
His family say he has bipolar disorder and was duped by a criminal gang into unwittingly carrying drugs for them.
The BBC's Quentin Sommerville said Mr Shaikh's relatives want to explain that he had "suffered from long-term mental illness" and travelled to China to pursue a "fantasy" belief in a possible career as a pop star.
"They believe he was not responsible for himself and certainly not responsible for drug trafficking," said our correspondent.
He added that the situation was getting "very desperate" for the Briton because the Chinese authorities do not have a reputation for leniency.
Soohail Shaikh says in his petition: "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."
Mr Stafford Smith said the Chinese Embassy authorities had been "kind" and opened on 26 December to facilitate a visa for this visit, "recognising the devastating blow that this execution date has inflicted on the entire family".
"We very much hope that this compassionate approach continues to the point of granting Akmal a reprieve," he said.
So far China has resisted calls to stop the execution, despite the case being raised by the UK 10 times during the last six months at senior diplomatic levels.
The prime minister has also written to China's leaders to express his dismay after Mr Shaikh's sentence was upheld by the Supreme People's Court.
If the sentence is carried out, it would be the first time an EU national has been executed in China for 50 years.