Many individual scientists at the US Environmental Protection Agency have dared to complain about political meddling in their work. Now we have an idea of just how widespread the censorship of science has become at the agency.

The Union of Concerned Scientists, a lobby group based in Washington DC, surveyed 1583 EPA scientists and found that many feel unable to speak openly for fear of retaliation from senior officials appointed by the Bush administration.

Over half said they were not allowed to talk freely with the media, while a quarter said they would not be allowed to publish results that contradicted the agency's official line. Researchers were often pressured not to publicly discuss issues linked to climate change, such as the coastal erosion caused by rising sea levels. The EPA did not respond to a request for comment.

But the survey does note some small victories for free speech. When one researcher was barred from talking about climate change at a conference, the meeting's organisers told the EPA that they would hold a 20-minute silence in place of the missing talk. The agency reversed its decision.