The high court will on Monday rule on a challenge by charities working with prisoners to the legality of legal aid cuts introduced by justice secretary Chris Grayling.

The Howard League for Penal Reform and the Prisoners’ Advice Service (PAS) say vulnerable people in the prison system, including inmates with mental health problems and mothers with young babies, will suffer injustice.

New regulations, introduced in December by Grayling, who is also the lord chancellor, remove the right to criminal legal aid in many prison law cases.

The charities accuse the minister of imposing the cuts in England and Wales for “ideological reasons entirely contrary to the rule of law” on inmates who will be “too vulnerable to complain”.

Their lawyers argued at a hearing in London earlier this month that the “unfair, irrational and inflexible” changes will undermine prisoners’ rights and their chances of rehabilitation, as well as cost the taxpayer additional millions because they will trigger “hidden costs”.

Justice Rafferty and Justice Cranston, sitting in London, are being asked to rule that the case raises issues that are “arguable” and should go to a full judicial review hearing.

Phillippa Kaufmann QC, appearing for both charities, said the changes will lead to “huge unfairness” as inmates no longer have access to legally-aided advice and assistance at hearings within the prison system.

Kaufmann said the cuts stop legal assistance for female prisoners facing reviews over eligibility for mother-and-baby units, and representation and advice for inmates facing segregation and placement in close supervision units.

Others affected included category A prisoners wanting to progress to lower categories and eventual release, as well as those with issues related to resettlement on leaving prison.

The QC also contended legal aid has been unlawfully removed from prisoners’ hearings involving the Parole Board where the board does not directly have the power to direct a prisoner’s release.

Kaufmann said: “People are not going to be able to adequately represent themselves. The cuts will also interfere with the right of access of prisoners to the courts.”

She added: “The secretary of state has made absolutely clear he doesn’t believe that prisoners should have access to legal aid to go to court about these matters.

“These are ideological reasons entirely contrary to the rule of law. He has created a system that is inherently unfair.”

James Eadie QC, appearing for the justice secretary, said all the arguments now being put in court about ministers “victimising and targeting of prisoners” had already been considered by Parliament, but the new regulations had been approved against a backdrop of the need for “financial stringency in the legal aid system because of scarce resources”.

Eadie said the “punchline” that the cuts were unfair did not work because Ms Kaufmann could not point to any lead cases of unfairness having actually arisen.

If there was unfairness at internal hearings or reviews in the prison justice system, or before parole boards, civil legal aid was available for complainants to use the safety net of seeking judicial review.

If prisoners needed extra help because of vulnerability or mental health issues “no doubt proper allowance will be made for that”, said Eadie.

He said the UK legal aid system “is pretty much at the top of the tree in generosity” compared with the rest of Europe, but it was now necessary to get the multi-million pound budget under control.

In reply, Kaufmann said judicial review was no answer because the changes in the system meant that, now prisoners were denied legal assistance, “no-one will know” if they are entitled to bring claims against the prison authorities.

She said: “These victims of unfair decisions will not know where to go. They don’t have any lawyers any more to help them.”