The Chinese corruption scandal surrounding GlaxoSmithKline grew murkier yesterday when it said senior executives had been sent a secretly-filmed sex tape of the company’s top manager in China shortly before Beijing opened its investigation into alleged bribery of doctors.

GSK confirmed the existence of a video of Mark Reilly with his Chinese girlfriend apparently filmed in the bedroom of his Shanghai flat using a covert camera installed without his knowledge. It was sent anonymously by email to several senior GSK executives, including chief executive Sir Andrew Witty, in March 2013 along with allegations that the company was paying kickbacks to doctors and officials for using GSK drugs, according to people familiar with the situation.

The revelation adds another layer of intrigue to a saga that has roiled GSK for more than a year, badly damaging its China business and posing broader legal and reputational risks for the UK drug maker.