"I was constantly harassed in prison over signing a thing that they call admission of guilt and a statement of remorse," Peter Humphrey was quoted as saying by The BBC after being deported to Britain yesterday.
"I never signed those documents because I did not admit to having committed that offence... Therefore they tried to extort the confession by withholding medical attention for my prostate condition," he said.
Lu Kang, a foreign ministry spokesman, denied Humphrey's claims at a regularly scheduled press briefing in Beijing today.
Humphrey and his wife Yu Yingzeng, a naturalised US citizen, were linked to a corruption case involving pharmaceutical giant GlaxoSmithKline (GSK).
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The couple ran an investigative firm which was hired by GSK to probe a sex tape of the company's then China boss and other issues shortly before the British pharmaceutical company itself became the target of a Chinese government investigation.
Humphrey, who is suffering from health problems, was released seven months early after being sentenced to two-and-a-half years in prison by a Shanghai court in August last year. Time served in detention was counted towards the jail term.