Half of people with diabetes are failing to keep control of their blood pressure, risking "damaging" complications, figures suggest.
The analysis of NHS data in England by Diabetes UK showed the number of people not hitting their target has been stuck at about 50% in recent years.
High blood pressure increases the risk of conditions such as heart disease, kidney failure and stroke.
The charity said people needed more support to control their condition.
People with diabetes are normally told to keep their blood pressure below 130/80, slightly lower than the target for the rest of the population.
Those at risk of exceeding the target can be given medication as well as support in improving diet and losing weight to get their levels down.
But the figures - based on the National Diabetes Audit, which covers nine in 10 people diagnosed with the condition in England - showed that just 50.7% of patients had control of their blood pressure.
The proportion was almost exactly the same as the previous year.
It means that if the figure was replicated across the UK, 1.4 million out of the 2.9 million people with the condition would be at risk.
Diabetes UK chief executive Barbara Young said: "It is extremely worrying.
"People with diabetes need to be aware that high blood pressure can have a hugely damaging effect on their health.
"But instead we are in danger of high blood pressure becoming the norm in people with the condition.
"This is one of the reasons they are experiencing record rates of stroke and kidney failure and are dying years younger than the rest of the population."
A Department of Health spokesman said it was vital for health professionals to ensure diabetic patients with high blood pressure got all the health checks recommended by the National Institute for Clinical Excellence (Nice).
He added: "Diabetic patients who have high blood pressure should also get advice and treatment to help them manage the condition that fits with their lifestyle."