The number of adults with diabetes has risen more than 65% since 2005, figures show.
Almost 3.5 million people in the UK are now living with diabetes, according to analysis of GP data for the British Heart Foundation (BHF).
In the last year alone, there has been a 3.5% rise in cases, while hundreds of thousands more people are undiagnosed with Type 2 diabetes, which is linked to obesity and unhealthy lifestyles.
The BHF is highlighting the issue because of the strong link between diabetes and heart attacks. Having diabetes doubles a person's risk of a heart attack.
Patient data for 2014/15 shows almost 3.5 million people are now diagnosed with diabetes. In the previous year, the figure was 3.3 million and two million in 2004/05.
To mark World Diabetes Day, the charity is announcing more than £3 million of funding for research into the link between heart disease and diabetes, plus new treatments for the condition.
It is hoped the work will look at diabetes and how blood vessels function, which will lead to new therapies to cut the chance of people with diabetes dying early from heart disease.
Professor Peter Weissberg, medical director of the BHF, said: "Diabetes is a major risk factor for cardiovascular disease. Up to four million adults in the UK have diabetes so treatments are urgently needed that can help prevent them suffering a deadly or disabling heart attack or stroke.
"Research we're funding is showing us how diabetes can affect the blood vessels and bring on disease. By understanding this process, we hope to develop medicines that can prevent this disease process or even reverse it."
Dr Richard Cubbon, from the University of Leeds, is hoping to find a new way to treat the blood vessel damage associated with diabetes.
He said: "We've known for some time that diabetes can be hugely damaging to the blood vessels and, in spite of modern treatments, we are currently unable to reverse that damage.
"We're studying a protein which could be involved in blood vessel repair. Our research could lead to new drugs that help to prevent the deadly heart attacks and strokes associated with diabetes."
The work comes as separate research from University College London (UCL) found that socio-cultural factors including time pressure, commuting time and where people live play a role in the risk of developing diabetes.
Experts know that living a healthy lifestyle and maintaining a healthy weight cuts the chances of developing Type 2 diabetes.
Chris Askew, chief executive of Diabetes UK, said: "The number of people with diabetes is rising at an alarming rate and every year there are more than 20,000 people who die tragically young as a result of the condition.
"Given the scale and the seriousness of the condition, it is vital that there is more research into better treatment and, ultimately, into finding a cure.
"Diabetes remains one of the biggest health challenges of our time.
"We must protect the health of the nation by taking urgent steps to get to grips with it or we will continue to see more and more people dying before their time."