The number of people with the condition is expected to hit 5 million by 2025 - up from 3.8 million today, because people do not take it seriously enough or make the right lifestyle changes, a charity said.
And less than a third of people realise that Type 2 diabetes can lead to serious health complications such as amputation, heart attack, blindness and stroke, according to Diabetes UK.
Type 2 diabetes patients do not produce enough insulin or the insulin they produce does not work properly. Roughly 85% of diabetes sufferers have Type 2 - it can be treated with exercise and an improved diet. Type 1 patients cannot produce any insulin, this strain is not caused by obesity and cannot be cured.
Diabetes UK has launched a national awareness campaign to have the risk of Type 2 diabetes assessed. Just 30% of the 1,000 people quizzed in an ICM Research survey knew Type 2 patients are more likely to go blind, while awareness that heart attacks (15%), amputation (28%), and stroke (7%) are complications of diabetes was even lower.
And just 13% knew that the condition increases risk of death, despite the fact that people with Type 2 diabetes are 36% more likely to die in any given year than someone their age who does not have the condition. Up to 80% of Type 2 cases could be prevented through lifestyle changes.
Barbara Young, chief executive of Diabetes UK, said: "This survey makes it clear that most people do not understand the potential consequences of developing it and I worry that until we finally lay to rest the myth that Type 2 diabetes is a mild condition, it will continue to be seen as something that is not worth being concerned about.
"This is a misconception that is wrecking lives and is the reason that as a country we are sleepwalking towards a public health disaster of an almost unimaginable scale."
A Department of Health spokesman said: "The number of people with diabetes is steadily growing, with often devastating consequences for their health. We are helping people make healthier choices to help prevent obesity which can lead to Type 2 diabetes.
"By working with industry we have helped to reduce fat, sugar and salt in foods, and thanks to the Change4Life campaign we are targeting more and more children and families with information on how to eat well, move more and live longer."
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