British pharmaceuticals giant GlaxoSmithKline is under criminal investigation by the Serious Fraud Office.
In a brief statement, the SFO said it is probing GSK's "commercial practices" and urged whistleblowers to come forward.
"GSK is committed to operating its business to the highest ethical standards and will continue to cooperate fully with the SFO," said the firm, which did not give details on what was being investigated.
GSK, the UK's largest pharma company, is already under investigation by Chinese authorities in a separate bribery probe. Three former GSK executives have been charged in relation to the investigation.
They are the ex-head of GSK's China unit, Mark Reilly, and two other executives, Zhang Guowei and Zhao Hongyan.
All have been accused of routing 3bn yuan ($488m, £307m, €365m) in bribes to doctors through 700 travel agencies and consultancies over six years.
GSK has said it takes all of the allegations made by Chinese authorities seriously. It had informed the US Department of Justice, the US Securities and Exchange Commission and the SFO of the China probe.
The firm admitted that some Chinese executives appeared to have broken the law, but CEO Andrew Witty said the head office had no prior knowledge about the wrongdoing.