City of London police are probing whether a landmark United Nations deal to supply life-saving drugs to Congo was marred by bribery involving two key contractors employed to help prevent corruption.

British and Danish investigators are examining about $1m (£563,000, €725,000) of alleged payments by Denmark’s Missionpharma, a leading supplier of generic medicines to poor countries, to a British-registered charity that advised the UN on the project, people familiar with the case said.