NHS Providers, which represents hospital trusts in England, fears lives could be lost because patients are being forced to spend long periods waiting in ambulances outside A&E, or on trolleys.

Hospitals are so “dangerously short” of beds that they may be unable to cope with the coming winter, Chris Hopson, the organisation’s chief executive, told the Observer. They will struggle even more than last winter – when chaotic scenes led the Red Cross to call the situation “a humanitarian crisis” – because a £1bn government initiative intended to free 2,000-3,000 beds by September has failed, he added.

That scheme aimed to reduce the proportion of beds occupied by patients who are fit to be discharged but cannot leave – called “delayed transfers of care” – to 3.5% of all beds by this month. It was 5.6% of beds at the end of 2016 and still 5.2% at the end of June, NHS figures show.

“That 3.5% target is going to be missed,” Hopson said. “Therefore, hospitals this winter will still be too full of people whom we can’t discharge, even though they are medically fit to leave, because of problems with social care. Failure to do so leaves us dangerously short of capacity.

“That means that it could be even worse than last year, when there were far too many patients waiting more than 12 hours on a trolley or in the back of an ambulance to be seen. We were running much greater levels of risk to patient safety than we had had for at least a decade and we don’t want to see that level of risk again.”

Hopson added: “If that does happen, it could result in patients having dreadful experiences. If people are ill, they need to be seen quickly or their condition gets worse or ultimately they die prematurely. Waiting unduly long can mean patients getting much iller than they should be and dying when they don’t need to.”

A new NHS Providers report details its concerns about winter.

In an online commentary for the Observer, Hopson writes that, despite efforts by the NHS nationally to plan for the cold spell ahead, “NHS trusts are worried that they do not have enough staff, beds and other services to manage the risk to patient safety this winter”.

The warning comes as some hospitals continue to struggle with the number of patients seeking help, even though winter is months away. Last Thursday the NHS trust which runs Royal Stoke University Hospital and County Hospital in Stafford asked people to stay away from their A&E units, except in a genuine emergency, to help reduce the “extreme pressures” on the units.

“Currently, both sites are experiencing the type of demand usually only see in the middle of winter, so people are experiencing long waits and our staff are exceptionally busy. Please only attend A&E Departments for anything classed as an emergency including choking, chest pain, loss of consciousness, severe blood loss, broken bones, difficulty breathing, deep wounds or a suspected stroke,” it said.

On Friday, Gavin Boyle, the chief executive of Derby Teaching Hospitals NHS Foundation Trust, wrote in his blog: “Without wanting to come over all Game of Thrones, winter is coming! For many working in our hospitals, it feels as though winter never went away and indeed August was one of our busiest months for emergency admissions.”

Also last week, University Hospitals of Leicester Trust put in place plans to improve its poor performance against the four-hour A&E target before the start of winter. These include increasing the number of doctors working overnight in A&E, a daily “safety huddle” of senior doctors, ensuring full staffing and managers monitoring how quickly the emergency department is processing patients.

Two trust bosses said that their hospitals are already facing major problems, especially because of staff shortages. “The first quarter of this year [2017-18] has been as challenging as any I can remember; there has been no let-up. Acuity, attendances and admissions have all stayed high,” said Nick Hulme, chief executive of Colchester Hospital University Foundation NHS Trust. “Our major concern going into this winter is staffing. Going into August we are 50 junior doctors short on our rotas across the hospital. Every day is a constant struggle for junior doctors and registered nurses.”

John Lawlor, his counterpart at the Northumberland, Tyne and Wear Mental Health Trust, said itsinability to arrange packages of care to enable patients to be discharged, resulting in beds being occupied unnecessarily, was “a significant concern. [In addition] pressures on staffing, especially in psychiatry, are beginning to impact on services and these will become more intense until the new people trained begin to come on stream over the next five to 10 years.”

The health service regulator NHS Improvement warned that hospitals had experienced “extremely high levels of bed occupancy” during April, May and June, despite those usually being the service’s quietest months. The regulator said it doubted that the plan for hospitals to return to treating the required 95% of A&E patients within four hours by the end of 2017 would succeed.

NHS England admitted that this winter would be tough, and revealed that hospitals were already planning to open at least 3,000 beds, which should help manage demand and minimise the risks to patients.

“The NHS will face challenges this winter, as it does every year, but NHS Providers have stated that winter planning is more advanced than it was last year and – as they argue – special attention is being paid to areas where pressures are likely to be greatest,” said Pauline Philip, NHSE’s national urgent and emergency care director.

“We are currently in the process of assessing how many extra beds trusts are planning to open over winter and early returns indicate that this will be more than 3,000. This is something we will continue to review on the basis of evidence rather than arbitrary estimates. If the expectations for reduced delayed transfers of care outlined by the government are achieved, this would free up a further 2,000 to 3,000 beds over the winter period, on top of the extra 3,000 plus beds that hospitals now say they’re going to open.”

The Department of Health was more upbeat about winter. “Thanks to the hard work and dedication of staff, alongside record levels of funding to ease pressure on A&E departments, the NHS has prepared for winter more this year than ever before, ensuring patients continue to receive safe and efficient care as demand increases,” a spokesperson said.