Children born in Britain are more likely to die before reaching their fifth year than in any other western European country apart from Malta.
Almost five in every 1,000 children born in the UK die before the age of five, according to a study in the Lancet medical journal.
Authors of the report said it was surprising for a country such as Britain, with free and universal healthcare.
Ingrid Wolfe of the Royal College of Paediatrics and Child Health told the Guardian: "These latest figures put us rock bottom of the western European league table."
Poverty and deprivation in the UK, together with cuts in welfare, were directly linked to the deaths of the youngest children, according to experts. Babies who die under age of one tend to be from poor households, have a low birth weight and with parents who smoked. Deaths between the ages of one and five are mostly linked to injuries, accidents and diseases such as cancer.
Last year, 3,800 under-fives died in Britain, a rate of 4.9 per 1,000 births. This puts the UK at 27nd place in Europe. Iceland has a child death rate less than half of Britain's.
Richard Horton, editor-in-chief of The Lancet said the reasons for the UK's high incidence of child mortality were varied but included "the poor organisation of children's health services in the UK."
He told the Times: "Until our politicians begin to take the health of children – the health of the next generation of British citizens – more seriously, new-borns and older children will continue to suffer and die needlessly."
Around the world, Guinea-Bissau in west Africa has the highest rate of child mortality – at 150 per 1,000. In 2013, more than 6.3 million children died before the age of five worldwide.
Singapore has the world's lowest child death rate at 2.3 per 1,000. Australia, Japan and South Korea all have better child survival rates than the UK.