PRETORIA -- Mr Justice William de Villiers' scathing criticism of President Nelson Mandela was not only an affront to the president's dignity, but raised serious constitutional issues likely to be the subject of drawn-out litigation and debate, experts said.

Judge De Villiers yesterday released a document containing the reasons for his ruling in favour of the South African Rugby Football Union (Sarfu) on April 18, when he set aside Mr Mandela's appointment of a commission of inquiry into the running of rugby.

The case provoked a furore when the judge ordered Mr Mandela to testify in person about his reasons for appointing the commission, a first in South African legal history.

The judgment has caused another outcry, and is expected to bring into sharp focus the debate about the transformation of a judiciary dominated by white judges who served under the apartheid government.

In his written judgment, Judge De Villiers found that Mr Mandela had not applied his mind when he appointed the commission. He had merely "rubber-stamped" a decision by Sport Minister Steve Tshwete, which was "grossly unreasonable" and unlawful.

The judge said Mr Mandela was an unsatisfactory witness with little credibility and some of his replies under cross-examination were "far-fetched". His most disparaging remarks were reserved for Mr Tshwete and his director-general, Mthobi Tyamzashe.

Mr Mandela's office said it objected strongly "to the belligerent tone of the judge's remarks. Unfortunately the nature of the remarks makes it impossible for any reasonable person not to believe the observations that were made about the history of the judge", presidential spokesman Parks Mankahlana said.

Judge De Villiers has been branded a racist for strongly opposing the admission of blacks to the Pretoria Bar while still an advocate in the 1970s. He also acted for the state in cases involving the rights of political detainees. He has been labelled a remnant of the apartheid regime.

"The president, however, appeals ... that, the attitude of the judge notwithstanding, nothing should be done or said to question the integrity and independence of our judiciary," Mr Mandela's office said.

The office was still studying the judgment, and a statement would be issued in the next 48 hours.

Mr Mandela's legal adviser, Professor Fink Haysom, said the government would take the matter on appeal to the Supreme Court of Appeals to challenge the ruling, the decision to call the president to testify and "certain procedural matters".

Mr Tshwete said: "Using the sanctuary of his seat, he set himself on a mission which, judging by his remarks, he must be satisfied he has accomplished. As to whose integrity -- mine or his -- needs to be examined, I leave that to history and posterity to decide."

Professor Gerrit Erasmus, constitutional scholar at the University of Stellenbosch, said the ruling raised important questions. While not disputing the right of the courts to review executive actions by the president, he said the question was how evidence about such actions should be brought before the court.

"To expose a person to this kind of treatment if you could obtain the same evidence through written statements is not a desirable development. What are the implications for the dignity of his office?"