The number of patients on hospital wards in England has been at unsafe levels at nine out of 10 NHS trusts this winter, BBC analysis shows.
To minimise the risk of infections and delays in getting treatment, hospitals are meant to have no more than 85% of beds occupied.
But the analysis showed 137 out of 152 hospital trusts have been above that level since the start of December.
NHS bosses said hospitals had major problems discharging frail patients.
One experienced hospital boss described some of the weeks this winter as the "worst" he had seen in his career.
Meanwhile, patients have been contacting the BBC to report the chaos they have experienced in overcrowded hospitals, including long waits for treatment and operations being cancelled at the last minute.
