Nursing associates being introduced across the NHS - who critics argue could be used as a cheap alternative to nurses - will be able to administer controlled medicines and carry out invasive procedures, documents suggest.

The Government has announced plans to create 2,000 nursing associate roles across England, with the first 1,000 due to start training at 11 test sites from December.

Health Education England (HEE), which is overseeing training, has said there has been "huge interest" in the role from hospitals and other parts of the NHS.

But Unison has warned the new roles should not be used "as a cheap way to replace registered nurses", and global safe staffing expert Linda Aiken, based in the US, has described the plan as "crazy".

Nursing associates are intended to bridge the gap between healthcare support workers and qualified nurses. Officials have said they will work "under the direction" of a fully qualified registered nurse.

The roles are also being billed as an opportunity for healthcare assistants to progress into nursing roles.

New HEE documents seen by the Health Service Journal (HSJ) show that nursing associates will be allowed to carry out invasive procedures on patients without the direct supervision of a qualified nurse.

They would also be allowed to calculate and administer controlled drugs.

The HEE documents say that by the end of two years of training, the " trainee nursing associate will be able to deliver planned nursing interventions... in a range of health and/or care settings under the direction of a registered nurse without direct supervision, delivering care at times independently in line with an agreed/defined plan of care".

It says they will be able to assess, plan, deliver and evaluate care, as well as recognise deteriorating patients.

Nursing associates will "correctly and safely undertake medicine calculations; administer medicines safely and in a timely manner, including controlled drugs". This will only happen where deemed appropriate and set out in organisational medicine management policies.

Associates will also be expected to be able to "correctly and safely receive, store and dispose of medications", the HSJ reported.

Anne Marie Rafferty, professor of nursing policy at King's College London, told the HSJ she was concerned about the proposals. She said: "It does not appear to be well thought through and is a recipe for confusion within the nursing profession, the public and other professions such as doctors about who is doing what in clinical practice."

In February, a s tudy led by King's College London and the University of Southampton found that hospitals with a higher number of healthcare support workers compared with nurses may have have higher patient death rates. Registered nurses looking after small groups of patients were linked to lower death rates.

Professor Peter Griffiths, from the University of Southampton, said his findings showed that a "policy of replacing registered nurses with support staff may threaten patient safety".

Researcher Jane Ball said: " Patients should not be asked to pay the price of receiving care from a less skilled and less educated member of staff, just to make up for the failure of the system to ensure enough registered nurses."

A BBC investigation last year found that some healthcare assistants were working without supervision, with some saying they had been left alone on wards with up to 40 patients, with junior staff asked to take blood samples and insert IV drips.

Lisa Bayliss-Pratt, director of nursing at HEE, told the HSJ that its document had been created as a guide for those institutions that will educate nursing associates "to ensure they provide what the NHS needs within their offer".

She added: "We have developed this framework as a result of wide consultation across the health and education systems, listening and responding to their needs to ensure this role plays a key part in a multidisciplinary team that focuses on quality of care.

"HEE's response to the consultation makes clear that this new role will support registered nurses and employers are expecting to deploy them as such."

Unison head of health Christina McAnea said: "These roles should not be treated as a cheaper alternative to registered nurses, for which there is still a desperate shortage.

"Unison will be closely monitoring the sites for the pilot schemes and supporting the trainees to make sure they are treated fairly."

Janet Davies, chief executive of the Royal College of Nursing (RCN), said: "The nursing associate role must not be a substitute for registered nurses, who are required to make clinical judgments using a high level of experience and knowledge to assess complex situations.

"Nurses are responsible for the wellbeing of their patients and this includes delegating some tasks to other members of staff.

"Part of their professional accountability involves making a judgment over when it is safe to delegate responsibilities to colleagues. To continue to do this properly they will need much more clarity over the roles and responsibilities of nursing associates.

"Safe administration of medicines is a key patient safety issue. Drug administration is not a mechanistic task - it requires professional judgment, and if ongoing assessment of a patient is required, it should be the responsibility of a registered nurse."

She said using unregistered staff to carry out nursing duties risks "reducing patient confidence in the health service".