Hong Kong’s judges, like their counterparts elsewhere, enjoy security of tenure. They cannot easily be sacked. This is an important safeguard of an independent judiciary, ensuring judges can decide controversial cases freely, without worrying about losing their job. But when a judge repeatedly falls short of the high standards the public rightly expects of the judiciary, action must be taken.Chief Justice Andrew Cheung Kui-nung took a bold but sensible step in securing the early retirement of Justice Wilson Chan Ka-shun, after the judge repeatedly plagiarised lawyers’ arguments in his rulings. Chief Executive John Lee Ka-chiu said he respected the decision. Chan is 64 and the usual retirement age is 70. Cheung honoured the security of tenure judges enjoy by requesting rather than demanding the judge step down. But Chan’s position had become untenable and it is no surprise he agreed.The judge was found to have extensively copied lawyers’ submissions into his judgments on multiple occasions. This led to appeals and sometimes new trials. He was severely reprimanded in 2023 but resorted to plagiarism again the following year.The judiciary took steps to help the judge, offering training and support. He was even, last year, moved to duties less likely to involve writing judgments. But another case of copying emerged in the Court of Appeal this month. Cheung described Chan’s conduct as “wholly unacceptable” and recognised the public concern. He said judicial copying “strikes at the very core” of the fundamental requirement that judges decide cases with an independent mind. Steps must now be taken to ensure cases handled by the judge, who was among those approved for national security trials, are not unduly affected.This is the first time a judge has departed the judiciary in such circumstances since Hong Kong’s return to Chinese rule in 1997. The Basic Law provides that judges can only be dismissed for misbehaviour or inability to carry out their duties. That would apply in extreme cases and requires a recommendation from a judicial tribunal.The temptation for judges to cut and paste or to fail to exercise their own judgment will grow with the increasing use of artificial intelligence. This must be avoided. The judiciary established guidelines on AI use in 2024, and should keep them up to date.