More than a third of adults in England have borderline diabetes, new research suggests.
If nothing is done to buck the trend, there will be a steep rise in diabetes, the authors said.
People are classed as having borderline diabetes, also known as pre-diabetes, when they have higher than normal blood glucose levels.
Those with the condition are at high risk of developing diabetes and its associated complications.
The prevalence of pre-diabetes in England has tripled in the space of eight years, according to the researchers.
Their study, published in the journal BMJ Open, found that in 2011, 35.3% of people had pre-diabetes - a steep rise from 11.6% in 2003.
The authors of the study examined data from Health Survey for England for the years 2003, 2006, 2009 and 2011 involving thousands of participants.
People were classed as having pre-diabetes if their glycated haemoglobin - a measure of blood glucose control - was between 5.7% and 6.4% and they had not previously been diagnosed with diabetes.
The results showed an "extremely rapid rise" in pre-diabetes, the researchers said.
People from poorer backgrounds were found to be at "substantial risk", they added.
"There has been a marked increase in the proportion of adults in England with pre-diabetes," they wrote.
"The socio-economically deprived are at substantial risk. In the absence of concerted and effective efforts to reduce risk, the number of people with diabetes is likely to increase steeply in coming years."
They added: "This rapid rise in such a short period of time is particularly disturbing because it suggests that large changes on a population level can occur in a relatively short period of time.
"If there is no coordinated response to the rise in pre-diabetes, an increase in numbers of people with diabetes will ensue, with consequent increase in health expenditure, morbidity and cardiovascular mortality.
"These findings are particularly problematic given the strong association of pre-diabetes with overweight and obesity, given the remarks by (England's chief medical officer, Professor Dame) Sally Davies that overweight and obesity had become the new normal in England."
They said the findings have important implications on the NHS Health Check and other public health interventions across England.
Barbara Young, chief executive of Diabetes UK, said: "Having high enough blood glucose levels to be classified as having pre-diabetes leaves people at a significantly increased risk of developing type 2 diabetes, which is a lifelong condition that already affects more than three million people and can lead to serious health complications such as heart disease, stroke, amputation and blindness.
"We need to make sure those at high risk are made aware of this so that they can get the advice and support they need to make the lifestyle changes that can help reduce this.
"In fact, up to 80% of cases of type 2 diabetes could be avoided or delayed by making these kinds of changes.
"Programmes such as the NHS Health Check are already doing an important job in assessing people's risk, by measuring weight and waist, as well as looking at family history and ethnicity. But at the moment not everyone who is eligible for this check is getting one and we need this to change.
"Some of this population may already be receiving treatment for high blood pressure or cholesterol but not all will and we are concerned that if people are being identified as being at high risk, or even having pre-diabetes, they may not be getting all of the support they need for their health to be managed effectively, including advice on weight reduction, activity and risk-reducing diet.
"A tenth of the NHS budget is already being spent on diabetes and unless we get much better at preventing type 2 diabetes this spending will soon rise to unsustainable levels.
"People can also check their risk online or at a pharmacy in the high street."
:: Diabetes UK urges people to check their risk of developing type 2 diabetes on its website: www.diabetes.org.uk/risk.