The 79-year-old handed himself in to police in July after a public stand-off, but his jailing, unprecedented for an ex-president, sparked violent protests and looting.

More than 300 people, mostly in Zuma’s stronghold of KwaZulu-Natal province, died in the protests.

The former leader had testified only once at the inquiry into what has become known as “state capture” – the allegation that government decisions were being taken on behalf of business interests through a corrupt relationship.

Zuma is also facing a separate corruption and fraud trial related to a 2019 arms deal.

Zuma has repeatedly said he is the victim of a political conspiracy.

Prison authorities say his release on parole was compelled by a medical report, but his ailment has never been disclosed.

He did, however, undergo surgery after he was imprisoned.

The former president’s spokesman said at the time that imprisonment had had “an exponential impact in terms of deteriorating his condition”. His lawyers also argued that their client’s illness had rendered him incapacitated.

South Africa’s main opposition party, the Democratic Alliance, which was part of the legal challenge against the decision to release Zuma from prison, welcomed Wednesday’s ruling.

“This is a big victory for the rule of the law and the principle of equality before the law,” its leader John Steenhuisen said.

The High Court in Pretoria ruled that the decision by the head of the correctional service Arthur Fraser, a known ally of Zuma, to release the former leader on medical parole was “reviewed, declared unlawful, and set aside”.

Lawyers representing Zuma have appealed against the court order, so there is no immediate prospect of him returning to prison.