A top doctor from Somerset claims emergency patients could be at risk because half of the country's A&E departments are understaffed.
Dr Clifford Mann, registrar at the College of Emergency Medicine and a consultant at Musgrove Park Hospital in Taunton, said hospitals were increasingly struggling to find enough medics.
He told the Mail on Sunday that junior doctors were unwilling to train to become emergency medicine specialists because of the intense workload and failure of hospitals to increase staffing levels to match the number of patients admitted.
The situation is worsened by the fact that 10 per cent of all full-time consultancy posts in the country's 220 A&E units are unfilled as many training in the NHS have preferred to go abroad to work.
He said the shortages will "undoubtedly" have contributed to the closure or downgrading of casualty departments.
"The key message isn't so much the vacancies out there, but that there's no one coming through to fill them," said Dr Mann, an emergency medicine consultant.
"We're striving to deliver a high-quality service but the job is seen as unattractive by junior doctors, and we are haemorrhaging trainees and suffering an unprecedented loss of consultants.
"A&E departments are the places most people use in a hospital – there were 20 million attendances last year – but they don't have the same level of resources as other areas.
"In surveys of trainee doctors by the General Medical Council, emergency medicine scores very badly for workload and work intensity compared with other specialisms. Junior doctors look at these surveys and think, 'I quite enjoyed A&E but it nearly killed me and I'm not sure I want to do it for 40 years'."
Dr Mann said he knew of several consultants who had quit to work abroad where conditions were generally better and financial rewards greater.
"The key is to make the job more attractive, which at the moment, with increasing numbers of patients and fewer staff than ever, is not a simple task," he added.
A Department of Health spokesman said the number of consultant emergency doctors had increased by more than 50 per cent in the past five years and that more patients who had minor injuries were treated by GPs and emergency nurse practitioners.
He added: "We have asked NHS and social services to assure themselves that they have capacity ahead of winter. This includes assurance over staffing in A&E departments."