Campaigners have told a High Court judge that “radical and significant” plans for the NHS could allow private firms to make decisions about healthcare.

The JR4NHS group is bringing a legal action against Health Secretary Jeremy Hunt over the planned introduction of accountable care organisations (ACOs), which they say “could easily be” for-profit companies.

The group was founded by three doctors and a university professor, and was supported by Professor Stephen Hawking until his death in March.

Prof Hawking had warned that introducing commercial companies to run parts of the health and social care system would amount to an “attack on the fundamental principles of the NHS”.

A judicial review by the four remaining claimants began before Mr Justice Green in London on Wednesday.

JR4NHS was founded by former consultant eye surgeon Colin Hutchinson, public health professor and doctor Professor Allyson Pollock, Graham Winyard, a former medical director of NHS England, and public management professor Sue Richards.

Lawyers for the four told the court they are, or were, “eminent in their respective fields” and brought the action because they are “deeply worried” about the plans and the absence of parliamentary scrutiny.

Jenni Richards QC, for the group, said: “They are concerned that ACOs have the potential to undermine the founding principles of the National Health Service and the principles set out in the NHS Constitution.

“They are particularly troubled that there has been very little discussion in, or consultation with, Parliament or with the general public.

“It is important to emphasise that… this claim is not concerned with whether ACOs are a good or bad thing, nor with the merits of the defendants’ collective policy of greater ‘integration’.

“The concern which prompted the issue of the judicial review claim was whether such a radical and significant change could lawfully be introduced and implemented without public consultation.”

Ms Richards said the group’s concerns were “in part vindicated” by an NHS England announcement in January that it intended to hold a 12-week public consultation.

She told the court ACOs would be given “responsibility” for delivering healthcare services for a decade, on a contractual basis, in each NHS region.

She said it was originally stated that ACOs would be allowed to “make most decisions about how to allocate resources and design care” for each local population.

However, the barrister said more recent statements of policy “may be said to hide or obscure what was previously explicit” and the Government had failed to set out its intention with “sufficient transparency or clarity”.

Ms Richards argued the plans for ACOs would involve an “impermissible delegation” of the functions of clinical commissioning groups (CCGs).

She argued that handing over the powers of “publicly accountable” CCGs to ACOs – which could be “private, for-profit bodies” – would be unlawful and said the ACOs would not be subject to the same checks and balances.

The case is being supported by the British Medical Association (BMA), which represents more than two-thirds of UK doctors, and campaign group Keep Our NHS Public.

Mr Hunt’s Department of Health and Social Care has rejected claims about ACOs as “irresponsible scaremongering”.

Lawyers representing Mr Hunt and the NHS Commissioning Board contend the case is “misconceived” and are urging Mr Justice Green to dismiss the claim.

They argued the ACOs were the result of a “lengthy process” intended to “improve patient services through greater integration of health and social care services”.

Fenella Morris QC, for the commissioning board, said: “The draft ACO contract expressly prohibits the provider from doing anything which would constitute unlawful delegation by a commissioner.

“This statement could not be clearer and is a powerful control on the actions of CCGs and ACOs.”

The hearing is due to last two days, following which Mr Justice Green is expected to reserve judgment.