The court had previously upheld an appeal by John Murphy, who taught at Claremont High. In a written judgment released this week, the three appeal judges say the council's disciplinary procedures were at fault. Members of the disciplinary committee were told of an earlier police warning which may have influenced their decision.
The judges state: "Justice must not merely be done, but must be seen to be done. In our opinion, even though the disciplinary committee may have applied the cor-rect test, justice was not seen to be done because members of the disciplinary committee had before them material which was irrelevant and which was prejudicial to the appellant."
The committee was not told to disregard the police warning and some members might have been influenced by it. Counsel for Mr Murphy had been informed that only the conviction would be taken into account. Mr Murphy and the GTC further disputed the availability of papers which the council claimed to have sent him.
Mr Murphy remains on the register and is eligible to teach. The GTC is considering the judgment but Ivor Sutherland, its registrar, said: "The ball is now in South Lanarkshire's court."
A spokesman for South Lanarkshire Council said Mr Murphy was "still on the pay roll".