The British Heart Foundation said that it is “simply unacceptable” that there are 5.5 million people in England living with undiagnosed high blood pressure.
The comments come as Public Health England encouraged people to “know their numbers” and find out what their blood pressure is.
Having high blood pressure can increase a person’s risk of heart attack, stroke and vascular dementia.
More than a quarter of British adults have high blood pressure, or hypertension, but the condition rarely has noticeable symptoms.
Public Health England is encouraging adults aged over 40 to get their blood pressure tested as part of their NHS Health Check.
Just 46 per cent of people invited to have their NHS Health Check - a free service for those aged 40 to 74 - have taken up the offer since it was rolled out in 2013.
But if the condition is identified as part of the so-called mid-life MOT, then those affected can get advice on how to reduce their blood pressure.
The health body said that diseases caused by high blood pressure cost the NHS more than £2.1 billion every year.
Simply increasing the number diagnosed by 15 per cent per cent would generate £120 million in savings each year, Public Health England said.
Professor Kevin Fenton, Public Health England’s director of health and wellbeing, said: “It is a serious problem when a disease that is largely preventable, like high blood pressure, is one of the leading causes of premature death and ill health in the country.
“We all memorise important numbers in our lives, whether it’s our PIN and telephone numbers or the latest football scores.
“Knowing your blood pressure number is an easy step to take that has the potential to save your life.”
Catherine Kelly, director of prevention, survival and support at the British Heart Foundation, said: “5.5 million people in England are living with undiagnosed high blood pressure, which puts them at a much higher risk of suffering a potentially deadly heart attack or stroke.
“For a condition which is so easily detected and managed, this figure is simply unacceptable and we need an urgent improvement in the number of people diagnosed with this silent killer.”
THe NHS Choices website states that if your blood pressure is too high, it puts extra strain on your blood vessels, heart and other organs, such as the brain, kidneys and eyes.
Persistent high blood pressure can increase your risk of a number of serious and potentially life-threatening conditions including heart disease, heart attacks, strokes, heart failure, peripheral arterial disease, aortic aneurysms, kidney disease and vascular dementia.
If you have high blood pressure, reducing it even a small amount can help lower your risk of these conditions.
The only way of knowing whether you have high blood pressure is to have a blood pressure test.
All adults over 40 are advised to have their blood pressure checked at least every five years. Getting this done is easy and could save your life. You can get your blood pressure tested at a number of places, including at your GP surgery and at some pharmacies.