GlaxoSmithKline has been found guilty of bribery by a Chinese court and has agreed to pay a fine of 3bn yuan (£297m) to the government in Beijing.

At the same time, the former head of its China division, Mark Reilly, and other GSK executives are facing two- to four-year jail terms, according to the state news agency, Xinhua. Reilly was accused of running a "massive bribery network".

The bribery case involved allegations that GSK sales executives paid up to 3bn yuan to doctors to encourage them to use its drugs. Other revelations included news that a sex tape of Reilly and his girlfriend was emailed to 13 company executives last year, including the chief executive, Sir Andrew Witty.

The company said the illegal actions of its subsidiary, GSK China Investment Co, were "a clear breach of GSK's governance and compliance procedures; and are wholly contrary to the values and standards expected from GSK employees". It has published an apology to the Chinese government and its people on its website.

According to its latest results, the scandal knocked four percentage points off GSK's sales growth in emerging markets. The company's staff have also been accused of bribing doctors in Poland, Iraq, Jordan and Lebanon.

GSK said it had fundamentally changed the incentive programme for its sales force, and increased the monitoring of invoicing and payments. Sir Andrew said: "Reaching a conclusion in the investigation of our Chinese business is important, but this has been a deeply disappointing matter for GSK. We have and will continue to learn from this. GSK has been in China for close to a hundred years and we remain fully committed to the country and its people."

Meanwhile, the Serious Fraud Office is conducting a criminal investigation into the drugmaker's sales practices around the world, including working with the Chinese authorities.

The US department of justice is also investigating GSK for possible breaches of the foreign corrupt practices act.