A report claims new mothers are not getting enough advice about breastfeeding their babies.
UNICEF UK said the health of mums and children is being put at risk by the continued failure to implement minimum standards of care.
Rates of breastfeeding in the UK are among the lowest in Europe, but nourishing a child in this way protects them against a range of illnesses, and helps guard women against breast and ovarian cancer.
Last year, the National Institute for Health and Clinical Excellence (NICE) said the NHS should put UNICEF's Baby Friendly Initiative in place as a "minimum standard".
It aims to support mothers by encouraging close contact, training staff and advising on topics such as expressing milk.
But according to UNICEF UK, many midwives and health visitors have little or no training in how to give advice on breastfeeding.
Sue Eardley, strategy manager at the Healthcare Commission, which monitors implementation of the guidelines, said: "Increasing breastfeeding rates has been shown to have significant benefits for babies and mothers, and the Baby Friendly Initiative provides a mechanism for ensuring staff are trained and provide a consistent message to women and their families."
The commission is currently conducting a review of maternity services in England, and will publish its findings next year.