People with diabetes are being refused blood glucose testing strips due to NHS rationing, according to a new report.
The Diabetes UK study found that people with the condition - who need to test their blood glucose levels several times a day - are having restrictions placed on how many strips they can have, sometimes by GP receptionists.
Many Clinical Commissioning Groups (CCGs), which have come under fire for rationing other NHS services, have guidance on how often people should test their blood glucose and how many boxes of strips should be issued per month.
They have also urged GPs to switch patients to cheaper blood glucose meters and cheaper strips (less than £10 for 50) - sometimes against the patient's will.
Diabetes UK said the rationing was a "false economy" because the cost of dealing with complications caused by poorly-managed diabetes, including stroke, heart disease, amputations and blindness, is far higher.
A Diabetes UK survey of more than 6,000 people found 25% had not been prescribed enough test strips for their needs.
A separate poll of over 1,000 people found 27% of patients had either experienced restrictions or been refused test strips, compared to one in five four years ago.
More than half (52%) of these had Type 1 diabetes, which is controlled by insulin.
The National Institute for Health and Care Excellence (Nice) recommends that all Type 1 patients self-monitor blood glucose levels, testing at least four times a day.
People who are frequent drivers, take regular exercise or who are at high risk of suffering low blood sugar may need to test up to 10 times a day. Illness such as flu can also cause erratic blood sugar levels and more testing.
The charity said it was also concerned that people with Type 2 have been told they do not need to test their blood sugar, despite those on insulin and some medications needing to.
The report said: "Budget constraints or 'excessive testing' were often the reasons given to people to explain why the restriction was occurring. People with diabetes found these restrictions stressful and had to make difficult decisions about when to test or not."
One patient said: " I was told they were expensive and we should test less. Only need to test four times a day. We use an (insulin) pump so need to test every two hours."
Another said: "They said I had my allowance for the month. There is a blanket limit on the number of test strips available to diabetics across the CCG."
Another patient said: "Doctor's receptionist told us we test too often", while another said: "I had to get my diabetes specialist nurse to ring my GP receptionist who was the one who questioned my use of strips on several occasions."
One said: "I feel annoyed that every week or so I need to keep ordering and that I need to justify myself to a surgery person that knows nothing about what we go through. '
The report said people were being forced into testing less, or were trying to buy strips online or via eBay, despite concerns about quality.
It also said some patients may not meet requirements set down by the Driver and Vehicle Licensing Agency (DVLA), which says some patients must test every two hours.
In the survey, 66% of people were also given no choice of blood glucose meter and had been switched to a different, cheaper meter, without any discussion with them.
Of these, 25% were not happy with the meter provided, including that it was was too large to carry around or did not upload the data to a computer.
Some patients were forced on to cheaper meters when their test strip prescription ran out, leaving them no choice but to accept a different meter.
Diabetes UK policy manager Nikki Joule said: "These short-sighted cost savings cause people real anguish and potential financial distress.
"It also means people are struggling to manage their diabetes, which can lead to serious consequences for their health, so we urge people to challenge restrictions and refusals.
"Local policies should allow sufficient choice and flexibility for individual circumstances to be taken into account when prescribing test strips and meters for people with Type 1 or Type 2 diabetes."
Professor Jonathan Valabhji, NHS England's national clinical director for diabetes and obesity, said: "Ultimately these are decisions for CCGs, but should be informed by best evidence and national guidance where appropriate.
"We need to ensure adequate provision and that clinicians take into account widely recognised Nice guidelines, which are clear about the need for test strips to support people in particular with Type 1 diabetes."