More than a third of parents lack the basic knowledge to make their children a healthy packed lunch for school, a survey suggests.
Some 36% of UK parents are unaware of NHS guidelines on what constitutes a healthy lunchbox, the poll of 5,000 adults for BBC Good Food found.
The guidance says a child's lunchbox should be based on starchy carbohydrates such as bread, potatoes, rice or pasta and include fresh fruit and vegetables, a source of protein, a sugar-free drink and a side dish such as a low-fat, lower-sugar yogurt.
Just 26% of parents from the North East and Cumbria said they followed the guidance, compared with 58% in London.
More than half of parents who are aware of the guidelines (54%) admit to only following them occasionally, with almost 10% admitting to packing leftovers - including last night's takeaway - for their children's lunch.
The top five most popular items regularly packed by parents for children's lunch boxes are sandwiches (88%), drink (71%), an apple (56%), crisps (51%), and a chocolate bar (25%).
The survey also found fewer Britons are cooking from scratch than ever, with almost one in five (19%) creating meals from two or more ingredients only once a week or even less frequently.
BBC Good Food editor-in-chief Christine Hayes said: "It's worrying to see from the report how many parents across the UK are unaware what a healthy lunchbox should contain.
"A balanced lunch provides the sustenance needed for the day and by keeping choices varied children are more likely to embrace eating healthily.
"Let's ditch soggy sandwiches and find exciting and nutritious alternatives that children will enjoy."