The warning came after two Co-op employees were jailed for three and a half years after being convicted of taking a £1 million bribe each.

A jury at Snaresbrook Crown Court in London found David Chambers, previously chief buyer at Co-operative Wholesale Services, and Allan Green, its former chief general manager, guilty of corruption.

They were convicted of taking the bribes to favour food supplier Hobson, which was seeking an extension to a contract in 1995.

Roy Ayliffe, director of professional practice at CIPS, said the case showed corruption can happen in Britain and has driven home the urgency to tackle it wherever it occurs.

He said the increasing importance of social responsibility worldwide and corporate transparency within the UK, Europe and North America, meant purchasers must understand what duties they have if they uncover corruption and bribery.

“The CIPS policy document Ethical Business Practices, adopted in January, says that where a professional purchaser uncovers any corruption, they have a duty to their profession and their employer to alert their senior management,” he told SM.

“They must do it or they are condoning it. To even hesitate is to condone it.”

But Ayliffe acknowledged it is often not easy for purchasers to accept the evidence they may find in their own department or organisation.

In February, the Anti-Terrorism Act made Britain the first country to outlaw corrupt practices such as facilitation payments, often described as monies paid to foreign government officials or firms to speed up services that would be done much later.