Unqualified support workers are practising in the NHS with job titles that describe them as nurses with advanced skills, experts have warned.
A new study found that thousands of nursing jobs across the NHS actually have titles that have little or no link to a nurse's education or level of experience.
Researchers said people are also working without being registered with the regulator, the Nursing and Midwifery Council (NMC).
In many cases, NHS trusts or staff themselves create their own job titles.
Professor Alison Leary, who led the study from the London South Bank University (LSBU), warned the practice could undermine public confidence in the profession and also puts patients at risk.
She said: "What the results of this study clearly show is that advanced nursing practice needs regulation to help protect the public.
"Lack of consistency has implications for the wider perception of advanced specialist practice in the worldwide community and the workforce more generally.
"If the current system is allowed to continue unhindered, then there is a real risk posed to patient safety.
"Public trust also risks being undermined by NHS trusts applying professional job titles to low-paid carers who are not fully qualified nurses.
"In some instances, there is evidence that these post-holders are being expected to treat members of the public and are missing diagnoses altogether, which could lead to patients becoming seriously ill or worse."
Prof Leary said it has been assumed that advanced practice job titles are associated with career progression but this is "unsound" and needs addressing by the NMC.
The research, published in the Journal of Clinical Nursing, examined 17,960 staff employed in specialist nursing jobs in the NHS over a 10-year period to 2016.
It found 595 different specialist job titles in use.
Researchers said the International Council of Nurses recommends that advanced level nurses who often prescribe drugs and manage a caseload have at least a Masters degree level qualification.
But of 8,064 posts examined by the team, for which educational data was also obtained, 323 (4%) were unregistered nursing support workers with titles such as 'advanced nurse practitioner' and 'specialist nurse', working in areas such as cancer and emergency care.
This is despite these staff having no formal first level nursing qualification registered with the NMC.
Meanwhile, among thousands more nurses registered with the NMC, those using the title specialist or advanced had a variety of qualifications, ranging from none to a Masters or PhD.
The NMC's chief executive and registrar Jackie Smith, told the Health Service Journal (HSJ) that NHS trusts had a duty not to mislead patients about who was caring for them.
She added: "If individuals are calling themselves nurses and they are not on our register, then from a patient perspective that is quite worrying."
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