New GP practice data have revealed that the number of people found to have diabetes has increased by more than 145,000 in one year.
More than 2.6 million people were diagnosed with diabetes in Britain, a rise of 145,499 in a year, the figures showed.
According to the charity Diabetes UK, the number who also registered as obese was more than 5.2 million, indicating that one in 10 are being treated for obesity, while one in 20 are undergoing diabetes treatment.
But figures could partly reflect GPs recording more patients with diabetes as they now receive extra money for monitoring diabetes sufferers.
Diabetes UK, however, said unhealthy lifestyles and obesity were indeed causing a rise in the number of those developing the condition.
Type 2 diabetes, linked to obesity and unhealthy diets, afflicts 90% of those with diabetes.
At the time of diabetes diagnosis, around eight in 10 people are overweight or obese.
Douglas Smallwood, chief executive of Diabetes UK, said the latest figures were "extremely worrying.
"Diabetes is a serious condition that causes heart disease, stroke, amputations, kidney failure and blindness, and more deaths than breast and prostate cancer combined."
He urged a spread of awareness of the condition and advised a balanced diet and active lifestyle to help reduce the risk of type 2 diabetes.