Britons should try to avoid bacon, sausages and other cured meats altogether as they are as big a cancer threat as cigarettes, experts have warned.

A major announcement by the World Health Organisation on Monday is expected to declare that processed meat is one of the most cancer-causing substances.

Separate Oxford research next month will show that eating just four portions a week increases the risk of bowel cancer by more than 40 per cent.

Academics yesterday urged the public to eat as little as possible and if they must have red meat, to stick to steaks, chops or a roast joint.

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Smoking: Scientists are believed to have agreed processed meat is ‘carcinogenic to humans’, the highest of five possible rankings, shared with alcohol, asbestos, arsenic and cigarettes

Processed meat has been preserved, for example by smoking, and includes ham and pate, as well as burgers and mince if they have been preserved using salt or chemical additives. Experts think the substances added during processing cause cancer. These include preservatives such as nitrates and nitrites – as well as substantial amounts of salt.

Fresh red meat is also strongly linked to cancer and the WHO is expected to categorise it one level below processed meat, as ‘probably carcinogenic’.

But it also provides many nutritional benefits and is high in protein, iron and vitamin B12, which prevent tiredness and infections.

Dr Rachel Thompson, of the World Cancer Research Fund UK, said: ‘If people can avoid it [processed meat], they should. It’s better to get what you need from fresh red meat.

‘Processed meat contains more salt and fat and there is likely to be a higher cancer risk from the actual processing.’

She added: ‘If there’s someone who has a bacon sandwich every morning and a ham sandwich for lunch, they are at higher risk. They should really try to cut down.’

Government guidelines introduced in 2011 recommend that adults eat no more than 70g of red or processed meat each day – equivalent to one small sausage or two rashers of bacon a day or one lamb chop every other day.

A spokesman for Public Health England, the government agency for preventing illness, said it would ‘consider’ the WHO’s guidelines as soon as they come out.

Ruling: The World Health Organisation is to list processed meat among the most cancer-causing substances, alongside arsenic and asbesto

A four-year study of 500,000 middle-aged men and women, by Oxford academics, found those who ate red or processed meat four or more times a week were 42 per cent more likely to develop bowel cancer than those who had it less than once a week. The research will be presented to the National Cancer Research Institute in Liverpool next month.

Experts think the chemical haem in red and processed meat damages the DNA of cells in the digestive system, triggering cancer. Surveys show four in ten men and one in ten women eat more than 90g of red or processed meat a day. The impending WHO announcement has caused alarm in the meat industry.

Barry Carpenter, of the North American Meat Institute, pointed out that almost every substance is deemed to pose some sort of cancer risk. ‘Scientific evidence shows cancer is a complex disease not caused by single foods and that a balanced diet and healthy lifestyle choices are essential to good health,’ he added.