Two in every three loaves of bread sold in the UK contain pesticide residues, according to a new analysis of government data by environmental campaigners. Tests on hundreds of loaves also showed that 25% contained residues of more than one pesticide.

The official tests are carried out by the government’s expert committee on pesticide residues in food (Prif) and the levels found were below “maximum residue level” (MRL) limits. The Prif experts concluded: “We do not expect these residues to have an effect on health.”

But Nick Mole, at Pesticide Action Network UK (Pan UK) and an author of the new report, said MRLs only indicate whether the pesticides had been applied to crops in the amounts permitted. “They are nothing to do with people’s health whatsoever,” he said. “There is the possibility of harm from the repeated ingestion of low doses of pesticides and no one has done research on the impact of the cocktails of pesticides we are all exposed to. We are all being experimented on without our consent.”

A major study on the differences between organic and conventional food reported by the Guardian on Friday concluded that pesticides were found four times more often on conventional fruit, vegetables and cereals. “If you want to avoid pesticides, the only sure way to minimise them is eating organic,” said Mole.

Pan UK analysed the pesticides residues reported by Prif in both supermarket own-brand loaves and top brand-name loaves. It found that 63% of the loaves analysed in 2013 contained traces of at least one pesticide and that contamination has run at these levels for at least a decade. The most frequently detected pesticide was glyphosate, a common weedkiller. The next most common were chlormequat, a plant growth regulator, and malathion, an organophosphate insecticide.

The chemicals were found in the bread significantly more frequently than in other foods, where on average 40% of products contain residues.

In March, the UK government produced a national action plan for pesticides, as required by EU law. It stipulates: “Member states should monitor the use of plant protection products containing substances of particular concern and establish timetables and targets for the reduction of their use”. However, the UK plan contains no timetable or targets, despite the area of crops being treated with pesticide being on the rise. David Bench, director of chemicals regulation at the Health and Safety Executive (HSE), which hosts Prif, told MPs in March: “We are not in favour of quantitative pesticide reduction targets as they are generally meaningless.” MPs criticised the HSE for “cherry-picking”.

Mole accused the pesticide companies, the Department for Environment, Food and Rural Affairs (Defra) and the National Farmers’ Union of having a “cosy” relationship. “The UK’s pesticide action plan was particularly weak,” he said. “Pesticides need to be used last, if at all, at the moment they are the first choice.”

A Defra spokeswoman said: “There is no human health risk from pesticide residues in bread. Levels of pesticide residue in food are minimal and we have strict testing methods in place to check this.”