The UK is set to inch upwards in global life expectancy rankings, rising from 26th place to 23rd by 2040, according to an international study on longevity and disease.

Despite being the fattest nation in Europe and rising infant mortality the average Briton can expect to reach 83.3 years old – up from 80.8 years today – according to Washington University academics.

The research published in The Lancet medical journal revealed Spain is set to top the life expectancy tables in 22 years time, with people living for an average of 85.8 years.

In the UK, and many other European nations, Alzheimer’s disease is set to overtake heart disease to become the biggest killer and the authors call for policy makers to act now and invest in research.

Life expectancy improvements in more developed nations are being undermined by rising levels of non-infectious disease caused by obesity and unhealthy lifestyles, the report warned.

Japan, the current frontrunner in the longevity stakes, is expected to slip to second, while the US is set to plunge from 43rd to 64th place as other countries life expectancies improve.

Despite being one of the richest nations in the world, US life expectancy is only set to rise by 1.1 years to 79.8 under the current predictions.

Although global life expectancy is expected to increase by 4.4 years on average, buoyed by gains in rapidly developing nations like China, there are still significant pockets of inequality.

While citizens in Spain, Japan, Singapore, and Switzerland can expect to live above the age of 85, average life expectancy for Lesotho, Somalia, Zimbabwe and the Central African Republic will be almost 30 years lower.

“Inequalities will continue to be large,” said Dr Christopher Murray, director of the Institute of Health Metrics and Evaluation (IHME) at Washington University.

“In a substantial number of countries, too many people will continue earning relatively low incomes, remain poorly educated, and die prematurely.

“But nations could make faster progress by helping people tackle the major risks, especially smoking and poor diet.”

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To carry out the study, researchers looked at the impact of 79 independent drivers of health including smoking, high body mass index (BMI), and lack of clean water and sanitation on causes of death around the world.

In 2016, the last time the study was carried out, four of the top 10 causes of premature death were non-communicable diseases (those not caused by infections) and injuries.

The new forecast shows that by 2040 this figure increases to eight. Heart disease, stroke, chronic lung disease, chronic kidney disease, Alzheimer’s disease, diabetes, lung cancer and road accident injuries are all expected to be in the top 10 causes of premature death by that date.