Bacon, ham and sausages rank alongside cigarettes as a major cause of cancer, the World Health Organisation has said, placing cured and processed meats in the same category as asbestos, alcohol, arsenic and tobacco.

The report from the WHO’s International Agency for Research on Cancer said there was enough evidence to rank processed meats as group 1 carcinogens because of a causal link with bowel cancer.

It places red meat in group 2A, as “probably carcinogenic to humans”. Eating red meat is also linked to pancreatic and prostate cancer, the IARC says.

The IARC’s experts concluded that each 50-gram (1.8-ounce) portion of processed meat eaten daily increased the risk of colorectal cancer by 18%.

“For an individual, the risk of developing colorectal cancer because of their consumption of processed meat remains small, but this risk increases with the amount of meat consumed,” said Dr Kurt Straif, head of the IARC monographs programme. “In view of the large number of people who consume processed meat, the global impact on cancer incidence is of public health importance.”

The decision from the IARC, after a year of deliberations by international scientists, will be welcomed by cancer researchers but it triggered an immediate and furious response from the industry, and the scientists it funds, who rejected any comparison between cigarettes and meat.

“What we do know is that avoiding red meat in the diet is not a protective strategy against cancer,” said Robert Pickard, a member of the Meat Advisory Panel and emeritus professor of neurobiology at Cardiff University. “The top priorities for cancer prevention remain smoking cessation, maintenance of normal body weight and avoidance of high alcohol intakes.”.

But the writing has been on the wall for ham, bacon and sausages for several years. The World Cancer Research Fund has long been advising people thatprocessed meat is a cancer hazard. It advises eating products such as ham, bacon and salami as little as possible and having no more than 500g a week of red meat, including beef, pork and lamb.

Prof Tim Key, Cancer Research UK’s epidemiologist at the University of Oxford, said: “Cancer Research UK supports IARC’s decision that there’s strong enough evidence to classify processed meat as a cause of cancer, and red meat as a probable cause of cancer.

“We’ve known for some time about the probable link between red and processed meat and bowel cancer, which is backed by substantial evidence.

“This decision doesn’t mean you need to stop eating any red and processed meat. But if you eat lots of it you may want to think about cutting down. You could try having fish for your dinner rather than sausages, or choosing to have a bean salad for lunch over a BLT.”

The statement from the IARC, published as an article in the journal Lancet Oncology, substantially toughens the line, especially against processed meat. But while cancer scientists are concerned about the risks of eating too much meat, some nutritionists maintain that the extra risk is relatively small and that meat has other benefits.

Dr Elizabeth Lund – an independent consultant in nutritional and gastrointestinal health, and a former research leader at the Institute of Food Research, who acknowledges she did some work for the meat industry in 2010 – said red meat was linked to about three extra cases of bowel cancer per 100,000 adults in developed countries.

“A much bigger risk factor is obesity and lack of exercise,” she said. “Overall, I feel that eating meat once a day combined with plenty of fruit, vegetables and cereal fibre, plus exercise and weight control, will allow for a low risk of colorectal cancer and a more balanced diet.”

Prof Ian Johnson, emeritus fellow at the Institute of Food Research, also said the effect was small. “It is certainly very inappropriate to suggest that any adverse effect of bacon and sausages on the risk of bowel cancer is comparable to the dangers of tobacco smoke, which is loaded with known chemical carcinogens and increases the risk of lung cancer in cigarette smokers by around twentyfold.”

The North American Meat Institute said defining red meat as a cancer hazard defied common sense.

“It was clear, sitting in the IARC meeting, that many of the panellists were aiming for a specific result despite old, weak, inconsistent, self-reported intake data,” said Betsy Booren, the institute’s vice-president of scientific affairs. “They tortured the data to ensure a specific outcome.

“Red and processed meat are among 940 agents reviewed by the IARC and found to pose some level of theoretical ‘hazard’. Only one substance, a chemical in yoga pants, has been declared by the IARC not to cause cancer.

“The IARC says you can enjoy your yoga class, but don’t breathe air (class 1 carcinogen), sit near a sun-filled window (class 1), apply aloe vera (class 2B) if you get a sunburn, drink wine or coffee (class 1 and class 2B), or eat grilled food (class 2A). And if you are a hairdresser or do shift work (both class 2A), you should seek a new career.”