The London-based multinational said in a statement that the Serious Fraud Office (SFO) has opened a "formal criminal investigation".
A spokesman for the company said: "GSK is committed to operating its business to the highest ethical standards and will continue to co-operate fully with the SFO."
GSK has been at the centre of a slew of allegations in recent months from investigators in China, Iraq and Poland after company reps were alleged to have paid doctors and hospital officials to prescribe its products ahead of others.
Earlier this month, Chinese police accused Mark Reilly, a senior executive, of pressing his sales team to bribe doctors, hospital officials and health institutions, allegedly resulting in "illegal revenue" of billions of yuan.
Reilly and two Chinese executives were also accused of bribing government officials in Beijing and Shanghai.
GSK whistleblower Jarek Wisniewiski told the BBC's Panorama programme last month that reps had paid doctors to boost prescriptions in Poland.
Another former GSK drug rep, who did not want to be identified, said they paid doctors for lectures that never happened and this would result in a greater number of prescriptions.
Panorama reported that a criminal investigation was under way and that 11 doctors and one GSK regional manager had been charged in connection with corruption.