The Institute of Economic Affairs has defended telling potential US donors they could get access to government ministers.

Greenpeace secretly recorded the think-tank's director, Mark Littlewood, saying they are "in the influencing game" and gave the recording to the Guardian newspaper.

The IEA told Today that donations were for research purposes and that it makes "no apology for seeking to raise funds".

The Charity Commission, which is already investigating the IEA, is expected to receive evidence from the Guardian and Greenpeace on Monday.