Doctors believe patients are being put at risk by being treated by advanced practitioners instead of qualified medics, according to shock new figures from the British Medical Association.
Meanwhile it emerged separately that almost half of NHS hospitals are using advanced practitioners or APs, who are usually nurses with additional training, to cover doctors' shifts with around one in four even using them to cover for senior doctors.
Four in five of more than 5,000 doctors surveyed by the BMA about the current use of APs in the NHS said patients were being put at risk while nearly a third (28%) saying the way APs worked in the NHS 'always' impacted patients' safety and nearly two-thirds (56%) saying it 'sometimes' did.
Over three quarters of the doctors - 3874 respondents - also agreed that the general public often did not realise they were not being treated by a doctor, possibly because of confusing job titles such as 'consultant clinical practitioner'.
Last year an AP, who was a 'consultant nurse', working for Rotherham NHS Foundation Trust, where 'senior advanced practitioners' are still allowed to cover registrar shifts, left the trust after an investigation found that 25 patients were harmed, seven fatally, after undergoing a complex endoscopy procedure at Rotherham General Hospital they carried out.
Use of the APs is in direct contradiction of NHS England advice which states they 'should not replace the roles of doctors'.
But across the UK, 48% of NHS trusts are using APs, who can be pharmacists, paramedics or physiotherapists, to fill in for junior doctors and 23% for registrars, senior doctors only just below consultant level.
NHS guidance says APs are 'not substitutes for more familiar professionals'.
NHS doctors have warned patients in hospital are being put at risk when they are treated by advanced practitioners.
The findings came after a Freedom of Information (FOI) request from the British Medical Association to NHS trusts across the UK.
The FOI revealed 41 of the 85 trusts who responded admitted using APs to cover doctors' shifts and 20 of those even allowed them to stand in for very experienced medics.
A similar proportion of trusts, 43 out of 88, told the BMA they now placed APs on medical rotas as standard, rather than on separate nursing rotas.
The FOI also revealed that APs working for North Cumbria NHS Trust could cover 'any grade with the exception of consultant' depending on competence while Lancashire Teaching Hospitals said APs in some departments could cover registrar roles if they were thought to have consultant level practice.
And Birmingham Women's and Children's NHS Trust said APs were on medical rotas as standard and were 'trained and employed to work in the same role as their medical colleagues' because there was 'no difference in role'.
'This means they do work on medical rotas which can be SHO [senior house officer - a type of junior doctor] or registrar depending on the speciality and level of training,' the trust responded to the FOI request.
Tom Dolphin, chairman of the BMA council, said that APs were being put in a position where patients' safety could be compromised because their hospital management 'could not fill a medical rota'.
He warned that the findings 'should be treated as an early warning light for everyone in UK healthcare'.
But defending their use, Lynn Woolsey, the chief nursing officer of the Royal College of Nursing (RCN), said that without advanced nurse practitioners, the health service would 'grind to a halt'.
Instead, she accused the BMA of attacking the sector through 'staged media interventions'.
A spokesman for the Department of Health and Social Care said APs were 'highly trained and play a central role in delivering care for patients, but are not replacements or substitutes for other roles'.