Peter Humphrey GSK
Peter Humphrey (left) and his former client GSK are under investigation by Chinese authorities.Reuters

Chinese authorities have formally charged a British-American couple with illegally obtaining and selling private information while in the service of British drugmaker GlaxoSmithKline (GSK) in China.

Prosecutors filed charges against British investigator Peter Humphrey and his American wife Yingzeng Yu at No. 1 Intermediate People's Court in Shanghai. This will require the couple to stand trial, reported state-owned Xinhua News.

GSK employed Humphrey's firm ChinaWhys in April 2013, to investigate the circulation of a sex tape of former GSK China head Mark Reilly with his Chinese girlfriend, as well as e-mails containing allegations of widespread bribery at the British drugmaker.

Authorities later detained Humphrey and his wife for illegally buying and selling private information, but have not yet made an explicit link between GSK and the case against ChinaWhys.

Authorities last month charged Reilly and other colleagues with corruption, after a government investigation found the firm made billions of yuan from elaborate schemes to bribe doctors

The couple were found illegally trafficking a huge amount of personal information on Chinese citizens, according to Xinhua. They allegedly traded household registration details, background of family members, real estate, vehicles, call log and exit-entry records of Chinese citizens.

In order to build a huge database, they illegally bought people's personal information from others, used secret photography, the charges allege.

They then allegedly sold reports on individuals at high prices to clients including GSK.

China's Ministry of Public Security had accused unnamed GSK executives of routing 3bn yuan in bribes to doctors through 700 travel agencies and consultancies over six years. In connection with the allegations, Chinese authorities had taken several GSK executives into custody and claimed a number of them admitted to criminal charges of bribery and tax law violations.

Reilly, who worked as GSK China's general manager, allegedly told Humphrey in April 2013 that accusations and information leaked about his activities was "groundless".

After the investigation on the informant, Humphrey found the bribery claim was valid and felt he was "betrayed and used", according to Xinhua.

Chinese state television had earlier aired a public confession from the couple who were arrested on 16 August 2013, but had made no mention of GSK then.