More than 2 million Britons are at risk of dying early because they have at least one potentially fatal illness, such as diabetes or high blood pressure, as well as coronary heart disease.

Research has revealed that 90% of the 2.3 million patients in the UK who suffer from heart disease also have another condition that could shorten their life – a total of 2.07 million people. More than half (57%) of the 2.3 million have at least three “multi-morbidities” – a total of 1.31 million people.

The British Heart Foundation (BHF), which commissioned the findings, said the growing number of people who have more than one serious illness “represents a grave challenge for a health system focused on treating individual illnesses”.

For example, 1.26 million people – almost six in 10 of the 2.3 million – have high blood pressure as well as coronary heart disease. There are 579,000 with diabetes, 313,000 have suffered a stroke and 284,000 also have heart failure.

NHS medical teams need to urgently improve their treatment of these 2.3 million medically very vulnerable patients in order to reduce the number of them who die prematurely and to reduce the health service’s costs of caring for them, according to the charity.

The NHS in England alone spends an estimated £7.4bn a year on treating cardiovascular disease, mainly heart attacks and strokes. But the wider economic impact of these conditions – which together are Britain’s biggest killer – has been put at £15.8bn.

“Over the years, we’ve made huge progress in improving survival rates for single conditions like heart attacks,” said Simon Gillespie, the BHF’s chief executive. “However, today’s figures point towards an emerging and very urgent challenge.”

The research was undertaken by the University of Birmingham’s Institute of Applied Health Research.

Its findings came as separate new findings showed that the number of patients living with heart and circulatory disease and at least five other illnesses rose sharply – from 6.3% to 24.3% – between 2000 and 2014.

Experts are baffled by the trend. Prof Sir Nilesh Samani, the BHF’s medical director, said: “More research is needed to understand the underlying reasons for the connections between different conditions, and why the number of people living with multiple diseases is rising at such speed.

“While factors like an ageing population, and the increasing number of people with conditions like diabetes is contributing, they don’t fully explain the trends we’re seeing.”