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."
The biggest ever public awareness campaign on Type 2 diabetes risk factors is being introduced, as health experts reveal that three million people in Britain have been diagnosed with diabetes.
Funds raised will help to pay for research into a vaccine for Type 1 diabetes as well as aiming to identify the 850,000 people in the UK who could be at risk from the condition.
The partnership between Diabetes UK and Tesco aims to provide information and advice to almost a million people with Type 2 diabetes, helping them to understand how to manage their condition.
Every year 24,000 people with diabetes die earlier than expected in England and Wales.
Urgent action is required to stop the problem of diabetes, a health organisation has warned.
Barbara Young, Chief Executive of Diabetes UK, said:
We are hugely concerned that the number of people diagnosed with diabetes has reached three million for the first time and there is no reason to think this will mark the end of what has been a rapid rise in the condition.
Instead, all the projections suggest that the three million figure will be a grim staging post on the road towards a public health emergency and this unfolding tragedy is already putting huge pressure on the NHS and will have potentially devastating consequences for those people who develop the condition. But this is not inevitable.
Three million Britons have been diagnosed with diabetes, research has shown.
It is the equivalent to 4.6 per cent of the population, and experts say the figure is growing, warning it was a "grim staging post towards a public health emergency".
Research by Diabetes UK and Tesco has found that more than 130,000 people were diagnosed with the disease over the last year, with an estimated 850,000 people thought to have undiagnosed Type 2 diabetes.
Health experts say that the NHS could be burdened with unsustainable costs, unless more is done to prevent it.
All adults aged 40 and above should have a risk assessment for type 2 diabetes, according to the healthcare watchdog.
The National Institute for Health and Clinical Excellence (Nice) has also recommended that people aged 25 and above of South Asian, Chinese, African-Caribbean or Black African descent, who are at a higher risk, should also perform a test.
People can be assessed at their GP surgery or community pharmacy but they can also perform self assessments online.
Diabetes costs the NHS almost £12 billion a year and it's getting worse, new research has found. Read ITV's Science and Medical Editor, Lawrence McGinty's blog, here.
– A Department of Health spokesmanWe are taking wide-ranging action to tackle diabetes. First through prevention - by encouraging healthier lifestyles and identifying those at risk and supporting them to take the necessary action to prevent diabetes. Secondly, by better management of the condition, both in hospital and in the community.
We hope to help prevent people getting diabetes in the first place, but by investing in the NHS and modernising it, we will also drive up the quality of care for those who have the disease.
There are two main types of diabetes, known as Type 1 and Type 2. Both types of diabetes are lifelong health conditions.
Type 1 diabetes usually develops early in life and is the most common type of diabetes in children. It occurs when the body is unable to produce any insulin.
Type 1 diabetes is treated with insulin injections, or by using an insulin pump. About 15% of people with diabetes have Type 1.
Type 2 diabetes is the most widespread form of the condition and usually develops later in life.
Type 2 diabetes develops when the body is unable to make enough insulin, or when the insulin that is produced does not work properly (known as insulin resistance).
Type 2 diabetes can be treated with diet and physical activity alone, or combining these with tablets.
The main symptoms of undiagnosed diabetes can include: