The charity Back Care has warned that heavy school bags could cause "an epidemic" of future back problems for the children who carry them.

Research showed that eight in 10 children in the UK regularly carry bags that are a fifth of their body weight on their backs. Dr Skew, vice-president of BackCare, said: "Children's skeletons are still developing, and having a heavy bag slung over one shoulder can exert unnatural force on the spine, muscles and attachments. Rather like exercising only one side of your body in the gym, you quickly get unilateral muscle-loading, which can cause the small muscles in the back to tighten and compress the spine."