Akmal Shaikh was arrested in north-west China in 2007
A British citizen sentenced to death for drugs trafficking in China is to plead his case at an appeal court.
Akmal Shaikh, from Kentish Town, London, was arrested on 12 September 2007 in Urumqi, north-west China.
He told officials he had no knowledge of the drugs he was discovered with, but was found guilty and sentenced on the same day in October 2008.
The Foreign Office said his appeal is expected on Tuesday, but it is unclear when the result will be announced.
It also said UK officials were "in touch at the highest level with the Chinese authorities".
The legal charity Reprieve says that Mr Shaikh, who is married with three children, suffers from bipolar disorder, a mental illness.
Reprieve says the court refused to allow Mr Shaikh to see a Chinese psychiatrist, and the charity's application for a psychologist to evaluate Mr Shaikh has been denied by Chinese authorities.
Reprieve's director Clive Stafford Smith said: "Akmal Shaikh faces the possibility of a hollow-point bullet to the back of the head sometime very soon, unless Gordon Brown makes strong representations to President Hu Jintao.
"And at a bare minimum, the prime minister can surely ensure that we get a mental health expert in to see Mr Shaikh, so we can prove the seriousness of Mr Shaikh's illness to the Chinese courts."
A Foreign Office spokeswoman said: "The UK government strongly opposes the death penalty in all circumstances.
"The UK government has already made representations to the Chinese authorities - representations continue in both China and London.
"Consular officials in China have visited our national since the pronouncement of the sentence, and most recently on 25 May."
The spokeswoman added that consular officials were working with Reprieve, among others, to ensure that Mr Shaikh received "appropriate legal representation".