Neil Heywood was murdered on the orders of a fallen Communist Party chief, according to the reports.
The Mail on Sunday quoted ''respected Mandarin-language websites'' saying Mr Heywood, 41, died from cyanide poisoning after allegedly having an affair with lawyer Gu Kailai, wife of Bo Xilai, seen until recently as a future leader of China.
Mr Heywood was found dead on November 15 in Chongqing, in central China.
Britain asked China to investigate his death and it emerged last week that Mrs Gu was being probed for ''intentional homicide''.
The newspaper said it was alleged that Mr Heywood was murdered after helping Mrs Gu to siphon nearly £800 million of assets overseas.