About 10.4 per cent saw readings rocket at a surgery when they were normal at home.
But experts say skewed readings could be as high as 25 per cent because anxiety at appointments can trigger a rise, known as white-coat syndrome.
They warn it could lead to over-diagnosis of high blood pressure and needless treatment.
In other cases, 3.6 per cent of patients were told their blood pressure was fine when 24-hour home monitoring found it to be high.
These patients were almost three times more likely to die young than a healthy adult, University College London researchers found.
About 12million have high blood pressure, a major trigger of heart disease and stroke.
The study of 63,000 adults, published in the New England Journal of Medicine, shows home monitoring equipment was 50 per cent more accurate than on-the-spot GP checks.
It was far better at predicting risk of heart death than GP tests.
Researchers say wider use of home monitoring would mean more patients getting suitable treatment sooner, saving lives.
Prof Bryan Williams, of UCL, said: “Home monitoring allows doctors to provide the most effective treatments at the earliest opportunity.”
But Prof Helen Stokes-Lampard, the chairwoman of the Royal College of GPs, said: “There is a significant cost involved.”
Source: Read Full Article