More than one in four ambulances are waiting outside London hospitals as they arrive with ill patients, new data reveals, as health leaders warned delays were causing “significant harm” to patients.

Nearly three in ten ambulances across England were left waiting in the past week, with ambulance chiefs warning the handover delays were leading to patients dying.

The NHS figures show that crews had to wait more than 30 minutes in 26 per cent of the 12,184 ambulance arrivals to hospital in the capital in the week up to November 20. Nearly one in ten (9.9 per cent) waited for more than an hour.

The target is for handovers to be completed within 15 minutes. Medics have warned the dire national picture is the worst start to winter since records began.

The figures provide the first weekly snapshot of how hospitals are performing this season, as the health service also struggles with a record backlog in care and looming industrial action by nurses.

Nearly a million Londoners were on a waiting list for routine hospital treatment at the end of September, according to figures published earlier this month.

Some 22,883 delays of half an hour or longer were recorded across all hospital trusts in England in the week to November 20, the figures show. This was 29 per cent of the 79,076 arrivals by ambulance.

A handover delay does not always mean a patient has waited in the ambulance as they may have been moved into an A&E department, but staff were not available to complete the handover.

Martin Flaherty, managing director of the Association of Ambulance Chief Executives (AACE), said: “These crippling delays are a twin threat - they cause significant harm to patients who are forced to wait in the back of our ambulances, while our crews are stuck and therefore unable to respond to patients who need us out in the community.

“As the colder winter weather approaches we have serious concerns that things will get worse in the coming weeks and months.

“The life-saving safety net that NHS ambulance services provide is being severely compromised by these unnecessary delays, and patients are dying and coming to harm as a result on a daily basis.”

A&E departments in the capital are also under serious pressure, according to separate figures analysed by the Standard earlier this month. A total of 8,102 people had to wait more than 12 hours in A&E departments in London in October from a decision to admit to actually being admitted, a doubling on the figure six months ago.

Waits of more than five hours to be admitted to A&E can significantly increase the risks of a patient dying or becoming seriously unwell, according to research published by the Emergency Medicine Journal.

Hospitals are struggling to discharge patients and free up capacity in A&E as many beds are occupied by patients in need of adult social care who have nowhere else to go. An average of 13,179 beds per day last week in England were occupied by people ready to be discharged.

This is slightly below the recent seven-day peak of 13,723 in early October, but is 25% higher than the number in the first week of December last year.

There was also an average of 344 patients per day in hospital with flu last week - more than 10 times the number seen at the beginning of last December.

Professor Sir Stephen Powis, NHS England’s national medical director, said the health service has “extensive” plans to deal with boosting bed capacity this winter, along with recruiting more call handlers and introducing 24/7 control centres to track and manage demand.

He added: “The first weekly data this year shows the considerable pressure faced by staff before we enter what is likely to be the NHS’s most challenging winter ever.

“Hospitals continue to contend with more patients coming in than going out, with thousands of patients every day in hospital that are medically fit for discharge, and so we continue to work with colleagues in social care to do everything possible to ensure people can leave hospital when they are ready.”

Matthew Taylor, chief executive of the NHS Confederation, the membership organisation representing the healthcare system in England, said the health service was heading into a “perfect storm”.

“Health service leaders have been warning for weeks that we are now facing one of the worst winters for decades. Sadly, this first tranche of winter data shows the NHS has not been crying wolf,” he said.

“These figures really hammer home just how stretched services already are as we head into a perfect winter storm. Significantly higher numbers of people are in hospital because of flu compared to this time last year, coupled with the fact that Covid-19 has not gone away.”