Peter Humphrey (R) and his wife [Photo/CCTV]

Foreign Ministry on Thursday denied the accusation that the British investigator working for drug maker GlaxoSmithKline Plc (GSK) and his wife were mistreated in Chinese prison.

Spokesperson Lu Kang said the allegation is not true.

"The relevant Chinese authorities acted in accordance with the law and guaranteed his rights," Lu said during a news conference, noting that the couple pleaded guilty and showed repentance during their imprisonment.

Lu said the authorities submitted a recommendation to the relevant court for commutation of the prison term. The court, after the examination, granted commutation to them in accordance with the law.

Peter Humphrey, 58, and his wife Yu Yingzeng, 61, were accused of illegally obtaining private information on Chinese citizens for clients, including GSK, through a consulting firm registered in Shanghai.

The couple were sentenced to two years in prison and fined 150,000 yuan ($24,165) in August. They returned to the UK on Wednesday evening.

In comments emailed to Reuters via a family friend, Humphrey said his requests for appropriate medical attention were deliberately obstructed by prison officers. He said he has prostate tumor and his wife a kidney disease.

Asked about Humphrey's claims of a forced confession, Lu said, "I am astonished about this. It seems that his stance was different before and after."

Humphrey's case unfolded alongside an investigation of GSK that led to a $489 million fine on the company and was the first time that foreigners were prosecuted for conducting an illegal investigation in China.