Fifteen government departments have been monitoring the social media activity of potential critics and compiling “secret files” in order to block them from speaking at public events, the Observer can reveal.

Under the guidelines issued in each department, including the departments of health, culture, media and sport, and environment, food and rural affairs, officials are advised to check experts’ Twitter, Facebook, Instagram and LinkedIn accounts. They are also told to conduct Google searches on those individuals, using specific terms such as “criticism of government or prime minister”.

The guidelines are designed to prevent anyone who has criticised the government in the previous three to five years from speaking at government-organised conferences and other events.

In September, the Observer revealed how three early-childhood education experts discovered that the Department for Education tried to cancel invitations for them to speak at government-funded events because they were judged to have been critical of government policy. Many more education experts and school staff have since uncovered files of their critical social media posts held by the department.