Increased breastfeeding could prevent around 800,000 child deaths and 20,000 adult deaths every year, a major new study has found.

It has also found that failing to breastfeed is costing the global economy around £210bn every year.

The Breastfeeding: Policy Matters study, published in the Lancet medical journal on Friday, shows only one in five children in high-income countries are breastfed to 12 months, while only one in three children in low and middle-income countries are exclusively breastfed for the first six months.

As a result, millions of children are failing to receive the full benefits provided by breastfeeding.

The UK has one of the lowest rates of breastfeeding in the world, with less than 1% of babies being breastfed to 12 months old.

The findings come from the largest and most detailed analysis to quantify levels, trends, and benefits of breastfeeding around the world.

It was carried out by scientists in Brazil and Switzerland with expert commentary on the findings coming from Dundee University.

The research was funded by the The Bill and Melinda Gates Foundation and the Wellcome Trust.

It claims that 13% of all deaths in children under two could be prevented by breastfeeding.

The authors of the report say breastfeeding is one of the most effective preventive health measures for children and mothers regardless of where they live but it has been overlooked as a critical need for the health of the population.

Professor Cesar Victora, of the Federal University of Pelotas in Brazil, said: "There is a widespread misconception that the benefits of breastfeeding only relate to poor countries.

"Nothing could be further from the truth. Our work for this series clearly shows that breastfeeding saves lives and money in all countries, rich and poor alike.

"Therefore, the importance of tackling the issue globally is greater than ever.

"Breastfeeding is one of the few positive health behaviours that is more common in poor than richer countries, and within poor countries, is more frequent among poor mothers.

"The stark reality is that in the absence of breastfeeding, the rich-poor gap in child survival would be even wider.

"Our findings should reassure policymakers that a rapid return on investment is realistic and feasible, and won’t need a generation to be realised."

The study claims that in high-income countries, breastfeeding reduces the risk of sudden infant deaths by more than a third, while in low-and middle-income countries about half of all diarrhoea episodes and a third of respiratory infections could be avoided by breastfeeding.

It also increases intelligence and might protect against obesity and diabetes in later life.

For mothers, longer-duration breastfeeding reduces the risks of breast cancer and ovarian cancer.

One factor cited by the researchers as a possible barrier to new mothers is the proliferation of breastmilk substitutes (BMS).

The authors claim laws to regulate the marketing of BMS have been "weakly" implemented, and "aggressive marketing of breast milk substitutes is undermining efforts to improve breastfeeding rates".

Frances Mason from Save the Children UK and Dr Alison McFadden from the Dundee University provided a comment on the findings.

They said: "Breastfeeding is too often siloed within agendas on nutrition or infant and young child feeding rather than treated as a key public health approach that can help prevent communicable and non-communicable disease prevention, reduce infant mortality, and lessen inequality.

"The active and aggressive promotion of BMS by their manufacturers and distributors continues to be a substantial global barrier to breastfeeding.

"The reach and influence of the BMS industry is growing fast. Global sales of milk formula (including infant formula and follow-on milks) have increased from a value of about $2bn in 1987 to about US$40bn in 2014.

"Political commitment, investment, and effective international, national, and local leadership are needed to end promotion of products that compete with breastfeeding."

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