There are thought to be 850,000 people who don not know they have type 2 diabetes.
A record breaking three million people have now been diagnosed with the disease, and experts are warning unless more is done to prevent the condition, the NHS could become burdened with unsustainable costs.
Diabetes sufferer Lynda Marks said dealing with the condition is much easier once you start talking about it.
She said: "It's difficult... to begin with."
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The figures by the Global Slavery Index are a third higher than previously thought.
Sara Di Pietrantonio, 22, died in Rome on Sunday.
A vote to remain in the EU will see Brussels exert more power over the NHS, according to the Cabinet minister.