Ham is one of the best-loved, staple fillings of the traditional British sandwich. Today, however, a leading charity has warned parents should not give children ham sandwiches in their packed lunch.

The humble ham sandwich. Along with cheese, egg and prawn, ham is one of the best-loved, staple fillings of the traditional British sandwich.

Today, however, as children across Scotland return to school from their summer holidays, a leading charity has warned parents should not give them ham sandwiches as part of their packed lunch.

Ham, along with other processed meats including salami, hot dogs and bacon, should be avoided by children, according to the World Cancer Research Fund (WCRF).

It cites "convincing evidence" that eating processed meat increases the risk of bowel cancer. While there is no specific research on eating the meats in childhood, the charity said the evidence in adults was too strong to ignore.

Children should therefore adopt a healthy eating pattern from the age of five and avoid processed meat, it said.

Marni Craze, children's education manager for the WCRF, said: "If children have processed meat in their lunch every day then over the course of a school year they will be eating quite a lot of it. It is better if children learn to view processed meat as an occasional treat if it is eaten at all."

Scientists estimate around 3700 bowel cancer cases could be prevented each year in the UK if everyone ate less than 70g of processed meat a week, which is roughly the equivalent of three rashers of bacon.

A recent survey showed that two-thirds of people in Britain were unaware that eating processed meat increases the risk of cancer.

The WCRF is also urging parents to avoid lunchbox fillers that are high in fat and calories. Foods such as sugary drinks can cause weight gain, and obesity in adulthood is linked to cancer, it said.

Ms Craze said: "With the large number of overweight and obese children in the UK, it is important that parents check the nutritional information on food to see if it is high in calories. If children are regularly eating high-calorie foods or sugary drinks they are more likely to become overweight.

"Putting ham or high-calorie snacks in your child's sandwich might seem like a convenient option, particularly for parents who do not have a lot of time to prepare their child's lunchbox. But packed lunches are a part of a child's diet that is relatively easy to control and it does not have to take too much time or effort to prepare a healthy lunch."

Ms Craze recommends unprocessed chicken, fish, hummus or low-fat cheese as quick and easy alternatives.

Jennifer Hynes, a registered dietician in Stirling who specialises in children's diets, said: "There is evidence that processed meat may contain cancer-causing substances and they could damage cells in the body, and could potentially lead to the development of cancer.

"I'd suggest that if your child likes ham sandwiches, you limit the number of times a week that you include them in a packed lunch.

"If you are very keen to reduce cancer risk, then you could avoid soaked or very processed hams - that is ones aimed at the children's market which might have faces on them.

"Basically, buy the best quality ham with the fewest additives that you can afford."