Pressure is growing on companies to come clean and explain themselves on political lobbying. Simon Zadek, chief executive of Accountability, a sustainable development think-tank, said: "Companies have not been looking at lobbying as part of their responsible business practice and they will need to do so in future."

Accountability, in association with the United Nations Global Compact, a corporate citizenship initiative established by the UN in 2000, recently published research into how private businesses influence public policy. The report said: "Responsible lobbying is the missing jigsaw piece in the corporate responsibility puzzle."