The Charity Commission has issued a regulatory alert to think tanks after calling into question their activities in recent months.
Earlier this year, the regulator ordered Legatum Institute Foundation to remove a report called Brexit Inflection Point for breaching political impartiality.
And last month, the regulator similarly ordered the Institute of Economic Affairs to remove a report about Brexit from its website because it was “not sufficiently balanced”.
On Friday, the Charity Commission published a regulatory alert and wrote to trustees of charity think tanks to remind them of their legal obligations and duties.
The alert says that campaigning activity “must further or support the charity’s objects and must not be party political”.
It says charity think tanks must be careful “not to support, or appear to support, a political party”. It says it may give an impression of impartiality if it consistently works with one party.
The alert says research produced by think tanks must not seek to change the law or change policy but must instead be designed to educate.
It also warns think tanks that they cannot waive responsibility for political opinions expressed by report authors if they are employees of the charity.
The alert adds that it is one of the trustees’ duties to make sure that the charity’s publications do not become used as political vehicles.
Helen Stephenson, chief executive of the regulator, said in her letter to think tank trustees: “Think tanks have an important role in society helping to educate the public.
“Society is richer when it is challenged with new ways of thinking and when debate is stimulated. However, think tanks which are charitable must operate and behave as charities.”