The Meteorological Office is blocking public scrutiny of the central role played by its top climate scientist in a highly controversial report by the beleaguered United Nations Intergovernmental Panel on Climate Change.
Professor John Mitchell, the Met Officeâ€™s Director of Climate Science, shared responsibility for the most worrying headline in the 2007 Nobel Prize-winning IPCC report â€“ that the Earth is now hotter than at any time in the past 1,300 years.
And he approved the inclusion in the report of the famous â€˜hockey stickâ€™ graph, showing centuries of level or declining temperatures until a steep 20th Century rise.
By the time the 2007 report was being written, the graph had been heavily criticised by climate sceptics who had shown it minimised the â€˜medieval warm periodâ€™ around 1000AD, when the Vikings established farming settlements in Greenland.
In fact, according to some scientists, the planet was then as warm, or even warmer, than it is today.
Early drafts of the report were fiercely contested by official IPCC reviewers, who cited other scientific papers stating that the 1,300-year claim and the graph were inaccurate.
But the final version, approved by Prof Mitchell, the relevant chapterâ€™s review editor, swept aside these concerns.
Now, the Met Office is refusing to disclose Prof Mitchellâ€™s working papers and correspondence with his IPCC colleagues in response to requests filed under the Freedom of Information Act.
The block has been endorsed in writing by Defence Secretary Bob Ainsworth â€“ whose department has responsibility for the Met Office.
Documents obtained by The Mail on Sunday reveal that the Met Officeâ€™s stonewalling was part of a co-ordinated, legally questionable strategy by climate change academics linked with the IPCC to block access to outsiders.
Last month, the Information Commissioner ruled that scientists from the Climatic Research Unit at the University of East Anglia â€“ the source of the leaked â€˜Warmergateâ€™ emails â€“ acted unlawfully in refusing FOI requests to share their data.