Health service chiefs have been declared “barking mad” for ordering hospitals to ensure no patient is treated in a corridor or languishes on a trolley for hours when this year’s winter crisis hits.

NHS England’s instructions, intended to avoid a repeat of hospitals’ descent into the sort of meltdown seen last year, also say that patients should not have to wait more than 15 minutes in the back of an ambulance outside an A&E unit as they wait to be handed over to hospital staff.

Critics have described the plans, outlined in a four-page letter sent to hospital chiefs as “la-la land”, “totally unrealistic” and an attempt “to create Narnia”. Hospital bosses say they regularly have to use all the three tactics which the NHS wants to ban in order to help them cope with the influx of patients created by winter weather and seasonal infections.

“We all aspire to avoiding doing any of those things. But trying to flog a dead horse, or to create Narnia, through a new set of executive instructions isn’t going to help us,” said Dr Taj Hassan, president of the Royal College of Emergency Medicine, which represents A&E doctors.

“Our urgent and emergency care system is under extreme stress going into winter. Given that hospitals are underbedded and underfunded, and emergency departments are understaffed, trying to deliver performance in that climate is nigh-on impossible. We have to define reality rather than delude ourselves about the scale of this problem of caring safely for patients during winter.”

One NHS trust chief executive, who spoke on condition of anonymity, said: “They are barking mad. Patients are waiting on corridors already. This will only get worse as we progress through winter. Twelve-hour trolley breaches in some hospitals are no longer unusual, and for some no longer cause distress or outrage as they are viewed as inevitable. The demands are not realistic.”

Disclosure of NHS England’s attempt to impose a detailed series of duties on hospitals comes amid claims by senior insiders that its leadership is in a state of panic over winter.

Theresa May has told Simon Stevens, the organisation’s chief executive, that he is “personally responsible” for how the NHS performs during what most expect to be a very tough winter, with a flu outbreak feared. Some NHS bosses believe that the prime minister’s move is intended to protect Jeremy Hunt, the health secretary, who they blame for underfunding it and presiding over huge staffing problems.

The regulator NHS Improvement warned last week that the service was already under such pressure, with hospital wards too full after the failure of a £1bn exercise to free up 2,000-3,000 beds, that it was in an “extremely challenging” position.

NHS England’s plans are laid out in a letter sent to all 233 NHS trusts and 209 clinical commissioning groups on 7 June by Pauline Philip, its national director of urgent and emergency care, headed “Winter briefing one: operational management of winter – expectations and communication”. Philip sets out actions “to consistently ensure that safety is maintained during times of significant pressure”. They include an edict that “clinical escalation will need to ensure that patients are not cared for on hospital corridors; 12-hour trolley waits in the emergency department never happen; [and] patients do not wait more than 15 minutes in ambulances before being handed over to the hospital”.

But hospital bosses claim their struggle to keep up with the sheer demand for care over winter, while maintaining patient safety, forces them to deploy the three practices Philip wants to end. Another chief executive said: “This is totally la-la land thinking. The pressure is mounting now. I don’t think any of the areas ‘to be avoided’ will be. Many chairs and non-executive directors of trusts are in complete disbelief about NHS England’s tone and approach.” Serious doubts have been raised about the ability of hospitals to do what Philip has asked. For instance, 1,597 patients had to wait at least 12 hours in an A&E unit to be admitted into the hospital itself in January to March this year, when cold weather caused a spike in illness that led to the NHS experiencing its most pressurised winter ever. So many hospitals struggled so much last January that the British Red Cross called the situation “a humanitarian crisis”.

NHS England, working alongside NHS Improvement and Public Health England, have made unprecedented joint efforts to ensure the health service can withstand this winter’s rigours. For example, NHSE has put £237m into a campaign to offer free flu jabs to a record 21m people including expanded numbers of primary schoolchildren and, for the first time, care home staff.

Chris Hopson, chief executive of NHS Providers, which represents trusts, said hospitals would do everything they could to avoid trolley waits or patients being treated on corridors, and minimise patient handover times between ambulance and A&E staff. But he added: “The indications are that flu may cause more problems than we have seen in recent years. And a prolonged cold spell – often linked to falls and respiratory problems – could make matters worse. So we need to be realistic and honest.

“Trusts cannot guarantee that these problems will not happen. What they can do – and are doing – is to have strong and well developed plans in place to identify when they are struggling to cope, so they can call on support to ensure patients get the best care possible.”