The private note records a discussion in 2010 between four scientists about how to persuade regulators to ban neonicotinoid pesticides.
The European Union imposed a temporary ban last year after the European Food Safety Authority identified risks to bees. The Department for Environment, Food and Rural Affairs opposed the ban, saying that there was not enough evidence of harm to bees.
Many British farmers have blamed the ban for high levels of damage to this winter's oilseed rape crop from flea beetle. Losses have ranged from 50 to 100 per cent in many fields.
The leaked note says that the scientists agreed to select authors to produce four papers and co-ordinate their publication to "obtain the necessary policy change, to have these pesticides banned".
A paper by a "carefully selected first author" would set out the impact of the pesticides on insects and birds "as convincingly as possible". A second "policy forum" paper would draw on the first to call for a ban.
The note, which records that the meeting took place in Switzerland on June 14, 2010, says: "If we are successful in getting these two papers published, there will be enormous impact, and a campaign led by WWF (World Wildlife Federation) etc.
"It will be much harder for politicians to ignore a research paper and a policy forum paper in [a major scientific journal]."
The scientists at the meeting included Maarten Bijleveld van Lexmond, chairman of the Task Force on Systemic Pesticides, and Piet Wit, chairman of the ecosystems management commission of the International Union for Conservation of Nature, an influential network of scientists and environmental groups.
The task force, a group of scientists who advise the IUCN, published a report in June stating that neonicotinoids were "causing significant damage to a wide range of beneficial invertebrate species and are a key factor in the decline of bees".
The task force used the report to call on regulators to "start planning for a global phase-out" of neonicotinoids. The present two-year EU ban, which began last December, is due to be reviewed next year using evidence from field trials.
Thousands of farmers who use neonicotinoids are hoping that the trials, overseen by the Centre for Ecology and Hydrology, will show that the risks to bees have been overstated.
Nick von Westenholz, chief executive of the Crop Protection Association, which represents Bayer and Syngenta, manufacturers of neonicotinoids, said "the work of the task force is regularly cited by activists as being strongly independent research, conducted with the utmost scientific rigour.
"From reading this document it looks to me that this group decided on its conclusions first and then embarked on the research to back them up.
"That clearly flies in the face of claims that the IUCN study represents independent and rigorous science.
"The claims of the task force now seem increasingly suspect and I hope that policymakers will treat these studies with an appropriate degree of caution," von Westenholz said.
Wit said that the leaked note was accurate but he denied that the scientists had decided the conclusions of the research in advance.
Dr. Bijleveld van Lexmond, a founding member of WWF in the Netherlands, said that the task force was independent and unbiased.