Complacency among both patients and staff is causing unnecessary asthma deaths, a national review has found.
Researchers found that asthma sufferers did not receive any medical help during their final attack in half of cases studied.
There were 1,242 deaths linked to asthma in 2012, meaning the UK has some of the highest rates in Europe.
By looking at 195 of these deaths, the National Review of Asthma Deaths found that the standard of care was “less than satisfactory” in a quarter of cases.
And there was “room for improvement” in the care received by 83% of patients.
Under-use of preventer inhalers was widespread, and too many patients relied on reliever inhalers.
And more than half of those who died were being treated for mild to moderate asthma. The researchers believe neither healthcare professionals nor patients recognized how serious the asthma was.
Kay Boycott, chief executive of the Asthma UK said: "This confidential enquiry has identified prescribing errors of a frankly horrifying scale and is a damning indictment of current routine practice."
"Past attacks are a clear risk factor for future attacks, but more than two-thirds of the people hospitalised in the month before they died did not get properly checked up afterwards.
"It's heart-breaking that the review has found 46% of deaths could have been avoided with better routine care."
Dr Kevin Stewart of the Royal College of Physicians, which managed the review, told the BBC: "It's time to end our complacency about asthma, which can, and does, kill. There are important messages in this report for clinicians, for patients and their families and for policy-makers.
"We haven't paid enough attention to the importance of good routine asthma care by clinicians with the right training and experience and the part that patients themselves play in this.”