Independent think tanks are being paid by companies to write policy reports and to gain access to senior politicians.

In the past year leading charitable think tanks have earned millions of pounds from private organisations that want to have influence in Whitehall, research by The Times has found.

The think tanks have commissioned research and published reports in areas of interest to their corporate sponsors and arranged events to discuss them with politicians. Some, such as Policy Exchange, have refused to publish details of their funders.

One senior figure at a think tank said that the arrangement allowed companies to “launder their interests” through independent groups with close links to officials. All the reports seen by this newspaper drew conclusions favourable to the companies concerned.