Foreign minister Ivan Lewis has made a last-ditch appeal to China not to execute Briton Akmal Shaikh.
Mr Lewis insisted it was "not right" that Mr Shaikh's mental health had not been taken into account when he was sentenced to death for heroin smuggling and urged Beijing to recognise the strength of feeling around the world.
But, speaking after meeting the Chinese ambassador in London, he admitted that the situation was now at "a very late stage".
Mr Shaikh, 53, from Kentish Town, north London, was convicted of smuggling 4kg of heroin after being arrested in Urumqi, north west China in September 2007.
The execution was due to take place at 2.30am on Tuesday but it is not yet known if it has been carried out.
"The clock is ticking and a man's life is at stake as we speak," Mr Lewis told reporters. "We hope that the relationship that we have with China will count for something in the end."
Mr Lewis said he had a "full and frank exchange of views" with the ambassador this evening.
"China fully understands the strength of feeling in this country and around the world," he said. "That strength of feeling focuses around Mr Shaikh's mental illness. It cannot be right that there has been no assessment done of Mr Shaikh's mental health."
Mr Lewis said the Government had now made 27 representations to the Chinese authorities in connection with the case over the past two years. "I believe we have now done everything that we possibly can," he added.
Mr Shaikh was informed on Monday morning that he would be executed on Tuesday as the Chinese authorities are said to have kept his fate from him up until then on "humanitarian grounds".
