Associates were introduced in the NHS 21 years ago with the expectation they would support doctors by delivering basic care.
Over the past two years the number of associates has more than doubled to 3,000.
According to the NHS Long Term Plan, there will be 12,000 physician and anaesthetic associates by 2036.
Fears have been expressed, however, that some have been acting beyond their original remit.
BBC News has seen evidence that in the month of Mrs Pollitt’s death, the NHS trust which oversees Royal Oldham used PAs to cover nearly 20% of doctor shifts in elderly care.
Several organisations, including the British Medical Association (BMA), have voiced concerns about the blurring of professional lines between doctors and associates across NHS trusts and primary care.
Anaesthetists United, a group set up by concerned doctors and consultants, has filed a legal claim against the General Medical Council (GMC) for not, in its view, properly defining associates’ roles and responsibilities.
One of the group’s founders, consultant anaesthetist Richard Marks, said patients were “being put at risk” as a consequence, something that “strikes to the heart of you” as a doctor.
BBC News has also learned that PAs have exceeded their remit in several NHS trusts, including by:
From December, associates will join doctors in being regulated by the GMC.
Significant concerns remain, however, from some within the medical profession.