A study predicts that Britain’s ageing and increasingly inactive population will dramatically increase pressures on health and social care Steve Debenport/Getty

More than two million older people will have at least four serious illnesses within 20 years because of the increase in obesity and lazy lifestyles, a large study warns.

Those in middle age are so unhealthy that as they get older two thirds of over-65s are forecast to have at least two conditions such as cancer, dementia or arthritis, up from half today.

Experts believe that past estimates of the rising cost of treating an ageing population are too low because they do not take into account this increasing level of sickness.

NHS chiefs like Simon Stevens have been calling for long-term reform of health and social care funding Stefan Rousseau/PA

Last night NHS leaders said that they would not cope without significant reform of the service.

Carol Jagger, professor of epidemiology of ageing at Newcastle University, warned that people were now reaching 65…