British Foreign Secretary William Hague has denied claims that Neil Heywood, who died in China last November, might have been a member of British intelligence.
It is unusual for ministers to discuss intelligence service matters, but Mr Hague said it was appropriate given the press speculation about Mr Heywood.
Gu Kailai, the wife of disgraced party chief Bo Xilai, is being held in connection with the case, which is being treated as murder.
Mr Heywood, 41, a businessman, was found dead in a hotel in Chongqing, south-western China, on 15 November. Officials initially said he died of excessive drinking.
Since then, there has been speculation in some media about whether he was involved with the intelligence services.