The NHS will draw on airline cabin crews to help staff the new Nightingale hospitals that are being constructed to cope with the wave of patients expected to need critical care as the coronavirus outbreak unfolds.

EasyJet has written to 9,000 UK-based staff, of whom 4,000 are trained in CPR, to invite them to volunteer for further training before helping out at the critical care field hospitals in London, Birmingham and Manchester.

Virgin Atlantic will contact 4,000 of its employees from Monday and prioritise those who already have relevant skills that can be put to good use at the sites. The volunteers will perform support roles, such as changing beds under the guidance of trained nurses, and will continue to be paid by the airlines.

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Work is under way to convert the ExCeL centre in London’s docklands into a 4,000-bed hospital, with an initial capacity for 500 beds with ventilators and oxygen. The hospital could open as early as this week. Two more Nightingale hospitals are being built at Manchester’s Central Convention Centre and the NEC in Birmingham.

Play Video 1:05 Worker posts video from ExCeL centre being converted into coronavirus hospital

But as volunteers for unskilled work flood in, doctors have expressed concern about where the specialist medics and nurses will come from. One London doctor who spoke to the Guardian said there would be no new staff, meaning those already working in NHS critical care would be spread even more thinly.

“It was all framed as if there would be a cavalry coming of newly upskilled doctors, doctors from other regions, and those out of retirement to staff it. But it is becoming more clear there is not a cavalry but just more space for us to spread into, but with the same number of staff,” the doctor said.

“At first the Nightingale felt like a great idea, as though a bunch of people would come to run it, but now we have realised it is robbing Peter to pay Paul and it feels more like a publicity stunt.”

Another medic who spoke to the Guardian said that critical care doctors and nurses in units across London had been asked to volunteer for the new coronavirus hospital.

Duncan Young, professor of intensive care medicine at Oxford University, said under normal “peacetime” conditions, a hospital has six to seven nurses per ventilator bed. A minimum of 500 to 1,000 experienced nurses would be needed to cope with 500 patients, he said, but only if the hospital ran well below recommended staffing levels.

“It will be really hard working at the ExCeL. It will be a high stress environment where the staff won’t know processes such as getting supplies, getting help, knowing where to send blood tests and so on, which are almost second nature at their home hospital,” Young said.

“I am not sure that upskilling nurses from other disciplines will work, not least because all the trainers are doing frontline work. A large number of similarly experienced doctors will be needed and one-fifth will develop Covid-19 and be off for a couple of weeks,” he added.

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Some volunteers are expected to be well-trained military intensive care nurses and doctors, who are largely based in Birmingham, but many are believed to have been pressed into service already.

Ruth May, the chief nursing officer for England, said: “Thousands of nurses, medics and other expert staff are returning to work alongside us, but we need everyone to do their bit – whether that is working in one of our current health or social care services, working in the Nightingale hospital, volunteering to help the NHS, or following government advice to stay at home, protect the NHS and save lives.”