60,000 unknown diabetics.
A survey of 3.6 million blood test records from GPs also revealed nearly half a million more are at risk of developing the dangerous condition.
Dr Tim Holt, of the University of Warwick, who led the study, said most undiagnosed victims had Type 2 which is linked to factors such as obesity.
Douglas Smallwood, chief executive of Diabetes UK, said: "We've been calling for years for active programmes to identify people with undiagnosed Type 2.
"Diabetes can lead to blindness, amputations, heart and kidney disease.
"The earlier people are diagnosed, the better."
The Department of Health said the study underlined the benefits of electronic patient records.