The French researcher who caused a scientific storm when he claimed to show that some GM food led to tumours and cancers in rats has accused the UK Food Standards Agency (FSA) of "recklessly endangering public health" by not demanding long-term testing of the foods.

In a series of parliamentary and public meetings held this week in London, Edinburgh and Cardiff, Prof Gilles-Eric Séralini has challenged UK politicians and safety authorities to review the way safety is assessed.

Séralini, a molecular biologist at Caen University, said: "Our research found severe toxicity from GM maize and [Monsanto pesticide] Roundup. The British Food Standards Agency has uncritically accepted the European Food Safety Authority's dismissal of the study, even though many of EFSA's experts have been exposed as having conflicts of interest with the GM industry. At the very least, the British government should demand long-term mandatory safety testing on all GM foods before they are released onto the market," he said.

"The British scientific authorities are deliberately misleading their government and are recklessly endangering public health in ignoring the findings of our research."

Séralini's study found that rats developed much higher levels of cancers and died earlier than controls when fed a diet of Monsanto's Roundup-tolerant GM maize NK603 for two years, or were exposed to Roundup over the same period. The usual industry tests last for 90 days.

The former member of two French government committees assessing the safety of GM foods suggested that the results could be explained by the endocrine-disrupting effects of the pesticide Roundup, and over-expression of the transgene in the genetically modified organism (GMO).

But although the €3.2m study was published in a peer-reviewed journal and claimed to be the most thorough long-term testing of GM food ever done, it attracted a torrent of criticism from the industry and some academics. It was refuted by several food standards agencies, including the UK's FSA as "biased, poorly performed, bogus, and substandard."

Monsanto, whose pesticide Roundup is engineered to be in most of the world's GM food crops, said it "did not meet minimum acceptable standards for this type of scientific research."

Séralini, in Britain for the first time since the paper was published, said he had been shocked by the "dishonesty" of many of his critics. "They reacted without checking anything. Mostly their quotes were stupid like 'GM has been used for years so it must be OK'. The fact that they were so violent suggested they had something to hide.

"I have been shocked at the conflicts of interests of so many scientists. There's much more than I thought. The problem is that there is a small group of scientists who attack you without checking the data for themselves. They do not demand the data from Monsanto."

But he said one year on his heavily criticised methodology is now being vindicated. A French government agency has called for tenders to repeat the experiment, and the EFSA has issued new guidelines to assess the risk of long-term toxicity from GM foods, which he said largely validate the way he conducted his experiments. EFSA has also accepted that no standardised protocol or guidelines exist.

However a spokesman for EFSA said: "EFSA's recent report has no implications on the authority's previous opinions related to the Séralini study and it should not seen as a validation of this study."

Séralini said: "I am not upset with GM, only the way it is controlled and assessed. It is bad for food. We are using the technology to make 'pesticide plants'. The way the technology is used is not neutral. I was in favour of GM. I am a molecular biologist. I believed it would reduce pesticides but I saw it did the opposite."

The problem, he said, was not just the pesticide, in this case Roundup, which is widely known to be highly toxic, but the GM process itself. "This was a landmark finding, to show that the GM 'event' itself is a problem. The GM is designed to produce enzymes which indirectly destroy the protective compounds in the plant.

"I am sorry that the link between GM and pesticides is not made. The GM allows more pesticide to be contained in the plant. Nearly 80% of GMOs are designed to absorb Roundup. The other 20% are designed to produce their own pesticide. We found that pesticides are not really tested."

The issue may not be resolved until both Monsanto and Séralini publish the raw data from their studies. "We have put our data in the hands of a notary and will release it as soon as they release theirs. Monsanto wants to know what data we have. They do not want a comparisonof my data to theirs. They want to hide their data.

"I discovered that their [Monsanto] historical data is wrong. They say to me 'you haven't looked at the historical data.' But I believe their historical data is contaminated. I believe Monsanto and the regulatory authorities have systematically underestimated the side-effects [of GM food]. All the regulatory tests are falsified by contamination of the data."

He said he wants his data to be compared. "That is the only way to show what I have done is 10 times better than they have. My data is just raw data. Theirs is important for the release and consumption of [commercial] food."

An FSA spokeswoman said: "This paper was reviewed by EFSA – and by a number of other regulatory bodies around the world – all of whom agreed that the results did not support these conclusions. EFSA's assessment has been backed by many other bodies who have carried out detailed reviews of the study and of the significance of the results. This includes the national food safety authorities in France, Germany, the Netherlands and Denmark. Our own scientists at the FSA agree with the points raised in these reviews.

"In relation to the claimed link between GM maize and cancer, the study used a strain of rats that is particularly prone to tumours. It is therefore not surprising that tumours were seen both in the GM-fed animals and in the non-GM fed controls. However, the number of animals used in the study was too small to determine whether there were significant differences between the two groups."