Triumphant DA leader Helen Zille has renewed her party's campaign to have Menzi Simelane removed from his position as national director of public prosecutions following a Supreme Court of Appeal ruling that declared his appointment unlawful.

Zille, who had taken the matter up on appeal after an unsuccessful application in the Pretoria High Court, said that though the judgment had to go to the Constitutional Court for confirmation, keeping Simelane in office was untenable .

"We don't think it's tenable, after a judge has said those things about the national director of public prosecutions, that he can continue to be in that position and take crucial decisions that will then obviously be open to question and challenge," said Zille.

Though Simelane and President Jacob Zuma might appeal the ruling, law experts said their options were limited .

Constitutional law expert Pierre de Vos described the judgment as "very sound in law" and unlikely to be overruled.

"They [the Constitutional Court] might interpret the facts differently but I would be shocked if, on the legal points, they came to a different conclusion."

The ruling could have dramatic consequences, De Vos warned, because, by extension, all decisions taken by Simelane during his tenure were invalid.

Law expert Shadrack Gutto said the ruling created an unprecedented situation - a painful one for Zuma.

"Once the Constitutional Court has made its ruling, the president has to abide by it."

Zille said the Supreme Court of Appeal "has now affirmed our original position. The president, in our view, appointed Simelane because he needed [a national director of public prosecutions who] had proved to be pliant to the wishes of the executive. This was part of the 'Zumafication' of the state institutions designed to shield the president and his network from being held accountable in law".

Zille said the ruling was a blow to moves by Zuma and his inner circle to use state institutions to fight factional battles in the ANC.

The Zuma administration was criticised this week for replacing the head of the Special Investigating Unit, Willie Hofmeyr, with Willem Heath, who formed part of a brains trust that helped the president fight off corruption charges in 2008.

"Now they have removed Willie Hofmeyr . they thought they could rely on Menzi Simelane . "

- Additional reporting by Sapa