Up to half a million patients could be put at risk every year as hospitals struggle to admit patients to hospital wards from bursting A&E departments, the College of Emergency Medicine has warned.

As many as 500,000 patients across the UK could see their situation deteriorate as a consequence of “exit blocking”, the college said. Exit blocking occurs when emergency doctors recommend that a patient should be allocated a hospital bed but they are unable to be admitted in a reasonable time frame.

The college, which speaks on behalf of doctors and consultants working in A&E departments in the UK, warned that patients can suffer as a result of crowded emergency departments.

“Crowding, where an emergency department becomes gridlocked, occurs in all emergency departments from time to time,” guidance issued by the college to hospitals states. “Crowding is associated with increased mortality.”

CEM president Dr Clifford Mann said: “This is such an important issue. It is about the flow of patients from ambulances, through A&Es and into hospital wards.

“The simple fact is that crowding kills. It is simply not acceptable to let this situation continue which is why we are speaking out to urge hospital chief executives and their boards to make sure they have plans to deal with this issue.”

 An NHS England spokesman said: “We are very aware of the pressures facing hospitals when patients need care but cannot access beds in a reasonable time frame.

“The extra £400m that we have released will help during this winter. In the longer term, our Urgent and Emergency Care Review is making recommendations to reduce crowding in the hospital system, improving the experience and outcome for patients.

“The specific problems raised by the College of Emergency Medicine are considered in our 2014-15 planning guidance.”