A review found last year that nearly 500 body parts had been retained by police without permission from relatives, with some dating back to the 1960s.

The new BBC investigation has uncovered that a large number of these belonged to children.

It found one mother was told police had kept the brain of her baby son, Rhys, died of a heart defect in storage at a hospital for 13 years.

Hannah Cheevers told BBC Radio Four’s Today programme that she only found out when two officers knocked on her door “totally out of the blue”.