Contingency planners were advised by the Met Office to expect a dry winter less than four weeks before the heaviest rainfall in 250 years.
The official guidance to expect “drier than normal” conditions was issued in mid November, just weeks before the onset of the wettest new year period on record.
The Met Office report, which claims to use “cutting edge science” to “help contingency planners prepare for and respond to emergencies”, predicted a pattern of high pressure weather systems would lead to dry conditions.
It added: “The weakening of the prevailing westerly flow means that the normally wetter western or northwestern parts of the country may see a significant reduction in precipitation compared to average, while the east or southeast may be closer to average.”
And the calculations of the Met Office's £30million supercomputer were spectacularly wrong after it predicted a slight 15% chance of the December to February period falling into a “wet category”.
The rogue report was part of a package of data and information that helped the authorities evaluate the risk of future flooding.
One of the country's leading flood experts, Paul Quinn of Newcastle University, explained: “This demonstrates the uncertainty of weather modelling, the only window of realistically forecasting the weather is a week at best and that is based on our knowledge and experience on what has happened historically.
“The only guidance a planner should use is to be prepared for the unexpected.”
And environmental contingency planner Martin Parr described the blunder as “appalling”.
“This information was incredibly inaccurate,” he added. “It is hard to believe that someone could have allowed this information to have been passed through to planners.
“We rely on accurate forecast information. All contingency planners are taught to expect the unexpected but we still require the right data to have the correct plans in place and the appropriate personnel and equipment in the right locations.
“This information was released from the Public Sector that should be relied on for accuracy – this was no use to neither man nor beast.”
A spokesman for the Taxpayers Alliance, said: “The Met Office paid out millions of pounds for a supercomputer capable of performing 1 billion calculations a second, how can we be sure that is delivering value for money.”