The Chinese authorities have stepped up their investigation into GlaxoSmithKline accusing it of being the ringleader of a half-a-billion-dollar bribery scandal involving 700 companies.

In a rare briefing to foreign media, Gao Feng, the lead Chinese investigator on a probe into the UK drugs group, said police were examining Rmb3bn ($500m) in deals from as far back as 2007. Chinese police believe that GSK used travel agencies and consultancies as a conduit to bribe doctors and lawyers in order to boost sales and profits, he said.

The UK-based pharmaceuticals giant said it had frozen all links with more than 20 Chinese travel agencies connected to the corruption probe and launched its own internal inquiry, describing the alleged practices as “shameful”.