The EU’s conclusion that a potentially dangerous weed-killer was safe to sell was partially based on scientific evidence that was written or influenced by Monsanto, the manufacturer of the product, an investigation by EUobserver and Dutch magazine OneWorld has revealed.

Earlier this year, a US court released a cache of hundreds of Monsanto’s internal emails that showed the firm’s involvement in at least two academic reports on glyphosate, sold under the trade name Roundup.

A Monsanto employee admits in one of the emails that the company wrote a study on glyphosate and later attributed the work to academics.

Another study on glyphosate was “redesigned” with help of company scientists in order to create a more favourable outcome, the internal emails suggest.

EUobserver and OneWorld have discovered that both of the studies were relied on by the European Food Safety Authority (EFSA) when it evaluated the safety of glyphosate in 2015 as part of the EU licence renewal process.

The documents, unsealed by an American federal court in California on 13 March, raise questions about the safety of the company’s flagship herbicide.

“You cannot say that Roundup does not cause cancer,” writes Monsanto toxicologist Donna Farmer in one of the emails, dated 29 September 2009. Farmer, who is writing to colleagues in Australia on how best to respond to a critical press report, says the chemical company has not done the necessary “carcinogenicity studies” to prove it.

Monsanto is facing around 225 lawsuits in the San Francisco court from people that claim that Roundup is the cause of non-Hodgkin lymphoma, a rare type of cancer. Most of the claimants are farmers who have worked with the weed-killer and fallen ill, or relatives of the deceased.