Professor Stephen Hawking has joined a legal action that is aimed at preventing greater privatisation in the NHS, in the latest phase of his ongoing dispute with Health Secretary Jeremy Hunt.

A lawsuit already exists that is seeking to prevent the establishment of what are called accountable care organisations (ACOs) in the NHS, which threaten to ration certain resources within the system.

Professor Hawking told the Guardian newspaper: “I am concerned that accountable care organisations are an attack on the fundamental principles of the NHS.

“They have not been established by statute, and they appear to be being used for reducing public expenditure, for cutting services and for allowing private companies to receive and benefit from significant sums of public money for organising and providing services.”

ACOs are commonplace in US healthcare systems.

In August Professor Hawking accused the Conservatives underfunding the NHS, and accused the Helath Secretary of misrepresenting research to provide misleading statistics about the organisation.

Mr Hunt claimed Professor Hawking was wrong to suggest the NHS was being turned into a “US-style insurance system.”

The lawsuit is intended to prevent the introduction of ACOs without them first being subject to parliamentary scrutiny.

“I am joining this legal action because the NHS is being taken in a direction which I oppose, as I stated in August, without proper public and parliamentary scrutiny, consultations and debate,” said Professor Hawking.

“I want the attention of the people of England to be drawn to what is happening and for those who are entrusted with responsibility for the NHS to account openly for themselves in public, and to be judged accordingly.”

Allyson Pollock, a professor of public health and one of the four people who instigated the legal action in October, said: “We are honoured and delighted that Prof Stephen Hawking, who cares so deeply about the NHS, is joining this legal action. The full details of these ACOs must be published and consulted on before they progress any further. This should be the first rule of good and transparent administration for the NHS.”

She added: “If Jeremy Hunt and Simon Stevens won’t budge, then this is the moment that everybody needs to come together and say clearly that the NHS is ours, and that we are going to fight to keep it that way.”

The Department of Health said: “We strongly resist the misleading claims in this action; it is irresponsible scaremongering to suggest that Accountable Care Organisations are being used to support privatisation and harm the fundamental principles of the NHS.