That means that almost 5m people are forecast to be morbidly obese across the three countries.
One of the study’s authors, Laura Keaver, said: “Morbid obesity – having a body mass index (BMI) of more than 40 - carries a higher risk of non-communicable disease and is associated with more complex health issues and challenges than obesity.
“This is likely to have serious health and financial implications for society and the UK health system.”
Previously obesity trends projected in the UK to 2035 made no distinction between obesity – BMI between 30 to 40 – and morbid obesity.
Welsh women aged 55-64 are projected the highest prevalence at 20% or one in five people in this age category.
The study looked at national surveys of body mass data from 2004 to 2014 across Scotland, England and Wales.
The study was published recently in the Scandinavian Journal of Public Health.