Five million people in England are at high risk of developing Type 2 diabetes, which is linked to obesity and unhealthy lifestyles, according to a new analysis.
In most parts of the country, more than one in 10 adults are at risk of Type 2 diabetes and, in some regions, the risk is around one in seven.
The new report, from Public Health England (PHE), is the most robust estimate yet of the number of over-16s with high blood sugar levels, known as non-diabetic hyperglycaemia, that could lead to Type 2.
Some 2.9 million people in England are already diagnosed with Type 2 diabetes, with obesity seen as a key driver.
A separate study found that encouraging weight loss and healthy living as part of a dedicated programme could prevent 26% of people with high blood sugar levels from developing Type 2.
The data is broken down by local authority for the first time ever, and ranges from 8.5% of people in Brighton and Hove being at risk to 14% in Harrow in north London.
High rates were also found in regions with large ethnic minority or older populations, which are known risk factors for diabetes.
A new programme - the NHS Diabetes Prevention Programme - will be launched next year with the aim of cutting the numbers developing Type 2.
It will focus on healthy eating, exercise and weight loss.
People identified through existing blood test results or an NHS health check as being at risk of Type 2 will be offered a place on the programme, which will last nine months.
Figures suggest that Type 2 diabetes already leads to 22,000 early deaths every year and costs the NHS around £8.8 billion.
Duncan Selbie, chief executive of PHE, said: "We know how to lower the risk of developing Type 2 diabetes: lose weight, exercise and eat healthily, but it's hard to do it alone.
"PHE's evidence review shows that supporting people along the way will help them protect their health and that's what our prevention programme will do."
Professor Jonathan Valabhji, the national clinical director for diabetes and obesity at NHS England, said: "There are too many people on the cusp of developing Type 2 diabetes and we can change that.
"The growing body of evidence makes us confident that our NHS Diabetes Prevention Programme will reduce the numbers of those at risk going on to develop the debilitating disease."
The diabetes programme commissioned the new data, which was compiled by PHE's National Cardiovascular Health Intelligence Network
Experts also analysed data from 36 studies and found that people supported by diabetes prevention programmes lose, on average, 1.57kg more weight than those not on a dedicated programme.
Barbara Young, chief executive of the charity Diabetes UK, said: "Having high blood glucose levels significantly increases your risk of developing Type 2 diabetes, which is a serious health condition which affects 2.9 million people in England, and can lead to devastating complications such as blindness, amputations and stroke, and ultimately early death.
"This is why it is really important that people at high risk of developing Type 2 diabetes are given evidence-based support to reduce their risk.
"As well as helping to reduce the human cost of Type 2 diabetes, this would also go a long way to helping to reduce costs to the NHS.
"The NHS spends 10% of its entire budget managing diabetes and unless we get better at preventing Type 2 diabetes, this figure will rise to unsustainable levels."
The report comes as the National Institute for Health and Clinical Excellence (Nice) published new NHS guidelines on managing diabetes in adults and children.
Its recommendations include same-day referrals of children and young people with suspected Type 1 diabetes to a specialist team to confirm diagnosis and provide immediate care.
It also called for better foot care for all people with diabetes to cut the risk of amputation.
Rachel Berrington, diabetes specialist nurse and Nice guideline developer, said: "Diabetic foot problems are serious, and if not managed appropriately they can lead to minor or major amputations and even death.
"Mortality rates after diabetic foot ulceration and amputation are high, with up to 70% of people dying within five years of having an amputation and around 50% dying within five years of developing a diabetic foot ulcer."