The independent study for the Department of Health found a number of trusts across England were converting midwife positions into posts for lesser qualified maternity support workers (MSWs).

Health Secretary Patricia Hewitt has always insisted that MSWs would not be used as substitutes for professionally qualified midwives.

But the report found they were doing tasks deemed within the role of midwives and requiring specialist midwifery knowledge and training.

The report said a lack of consistency in the training and role of MSWs had the potential to leave midwives and hospital managers uncertain about their competence, and placed patients at risk from a low standard of care.

King's College London, which surveyed trust managers across England, noted there was no statutory requirement for MSWs to undergo training, or any regulation to ensure public protection.

Midwives currently have legal responsibility for the work of MSWs, but systems to enable them to fulfil this task were variable, the report said.

It recommends a national framework to set training and standards for MSWs, and said the skills and tasks that could be delegated to them needed to be urgently identified.

The NHS collected little data on the cost-effectiveness of MSWs, and the report called for scrutiny where they were being trained to take on complex new roles.

The survey found MSWs made a "key contribution" to maternity care, and managers were "enthusiastic" about their role, reporting that they freed up midwives to spend more time with women and babies.