The research, published in the BMJ and led by Professor Trisha Greenhalgh and Professor Martin McKee, was written to inform the ongoing government-commissioned Leng Review which is examining the effectiveness and safety of these roles in UK healthcare.

The study found almost no research on patient safety and many studies involving fewer than 10 PAs.

The review's key findings are:

• Research on PAs and AAs in the UK is very limited. Only one small study assessed the competence of PAs through direct observation and no studies directly assessed the safety of AAs. Few of the studies screened for this research were of sufficient quality and relevance to current NHS policy and many studies were small, outdated, or lacked rigorous methods, making it difficult to assess the safety, effectiveness, or impact of PA and AA roles.
• Safety concerns remain unaddressed. No research examined safety incidents or prescribing safety and there is no robust evidence assessing PA and AA roled in managing high-risk or complex patients (for which their relatively limited training may not equip them).
• What evidence exists is limited to a few settings.  There was some preliminary evidence that PAs could support hospital ward teams and emergency departments when undertaking carefully circumscribed roles and closely supervised. However, evidence suggests PAs struggled in primary care, where the role is more autonomous and clinically complex. There is no direct evidence supporting the value of AAs in anaesthetics.
• There is no evidence that deploying PAs or AAs improves efficiency or saves money. As a senior doctor is needed to oversee and check the work of PAs and AAs, this model may be more expensive than employing doctors.
• Many patients were unaware they were seeing a PA, raising concerns about transparency and informed consent.
• Staff and professional bodies continue to express concerns about the scope of practice, supervision needs, and overall impact on medical training.
• Calling for evidence-based workforce planning.

Professor Greenhalgh, lead-author of the study and Professor of Primary Care Health Sciences in the Nuffield Department of Primary Care Health Sciences, University of Oxford, said: ‘The expansion of physician and anaesthetic associates should be informed by solid empirical research. At present, we simply do not have the data to support claims that these roles improve efficiency or maintain patient safety. The absence of reported safety incidents in research studies does not mean they do not occur - it means we are not doing the right kind of research to detect and analyse them.'

Professor McKee, co-author of the study and Professor of European Public Health at the London School of Hygiene and Tropical Medicine, added: ‘The mismatch between policymakers' enthusiasm for expanding these roles and the lack of rigorous research evidence should be a red flag. Workforce shortages are a real challenge, but they cannot be addressed by replacing doctors with people whose training maps poorly to the duties expected of them, and who may be inadequately supported, without a clear, evidence-based strategy.'

The study calls for a national scope of practice for PAs and AAs, informed by rigorous research into their safety, efficacy, and cost-effectiveness. Specifically, it urges:

• A systematic investigation into safety incidents involving PAs and AAs.
• Robust studies evaluating their impact on patient outcomes.
• An assessment of the hidden costs and inefficiencies associated with their deployment.
• Clear national guidelines defining their roles and limits, based on a detailed understanding of what their training prepares them for, especially in complex cases.

As the Leng Review deliberates on the future of these roles in the NHS, this study provides a crucial evidence-based perspective.