Processed meats - such as bacon, sausages and ham - do cause cancer, according to the World Health Organization (WHO).

Its report said 50g of processed meat a day - less than two slices of bacon - increased the chance of developing colorectal cancer by 18%.

Meanwhile, it said red meats were "probably carcinogenic" but there was limited evidence.

The WHO did stress that meat also had health benefits.

Cancer Research UK said this was a reason to cut down rather than give up red and processed meats.

And added that an occasional bacon sandwich would do little harm.

Processed meat is meat that has been modified to increase its shelf-life or alter its taste - such as by smoking, curing or adding salt or preservatives.

It is these additions which could be increasing the risk of cancer. High temperature cooking, such as on a barbeque, can also create carcinogenic chemicals.

How bad?

The WHO has come to the conclusion on the advice of its International Agency for Research on Cancer, which assesses the best available scientific evidence.

It has now placed processed meat in the same category as plutonium, but also alcohol as they definitely do cause cancer.

However, this does not mean they are equally dangerous. A bacon sandwich is not as bad as smoking.

"For an individual, the risk of developing colorectal (bowel) cancer because of their consumption of processed meat remains small, but this risk increases with the amount of meat consumed," Dr Kurt Straif from the WHO said.

Estimates suggest 34,000 deaths from cancer every year could be down to diets high in processed meat.

That is in contrast to one million deaths from cancer caused by smoking and 600,000 attributed to alcohol each year.

Red meat does have nutritional value too and is a major source of iron, zinc and vitamin B12.

However, the WHO said there was limited evidence that 100g of red meat a day increased the risk of cancer by 17%.

An eight ounce steak is 225g.

The WHO said its findings were important for helping countries give balanced dietary advice.

Little harm

Prof Tim Key, from the Cancer Research UK and the University of Oxford, said: "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.

"Eating a bacon bap every once in a while isn't going to do much harm - having a healthy diet is all about moderation."

The industry body the Meat Advisory Panel said "avoiding red meat in the diet is not a protective strategy against cancer" and said the focus should be alcohol, smoking and body weight.