Chief Justice Sundaresh Menon has made clear that parity in sentencing is important to preserve and protect public confidence in the way justice is administered.

His remarks underscored an appeal case in which a co-offender who played a more serious role in rioting and harassment offences was placed on probation, while the appellant was given a tougher sentence of reformative training.

It emerged that the district judge who sentenced the latter, Chong Han Rui, was unaware of the former's conviction by a different judge the previous month.

Chong pleaded guilty to the two charges last June. The district judge discounted probation based on the aggravating factors and seriousness of the offences, among other things.

Given pre-sentence reports, inadequate and suspect family support, the judge ruled reformative training as the most appropriate sentence.

Chong appealed through lawyer Justin Tan to the High Court where the Chief Justice was "troubled" to find that Chong's co-accused, "B", was given probation although "B was the more culpable offender ".

Among other things, B was the instigator, while Chong was a follower who did not show the same degree of disregard for the law.

The Chief Justice ruled that Chong should not be punished more severely than B. He said co-offenders should ideally be sentenced together by the same judge. But if it is not possible, the prosecution should tender to the sentencing court all relevant material in relation to sentences meted out to co-offenders.

In judgment grounds released yesterday, he explained that the crucial issue in applying the parity principle "is not whether a co-accused has been treated more leniently, but whether the public would perceive that the appellant had suffered injustice", citing a 1989 British case.

He wrote: "Public confidence in this context demands that sentencing is carried out with due regard to the element of basic fairness. Where this is not the case, and where co-offenders in a common criminal enterprise are sentenced in an unduly disparate manner, the sentences would then seem to be arbitrarily imposed and this raises fundamental rule of law concerns."

In allowing the appeal, he sentenced Chong to 27 months of intensive and supervised probation with conditions attached.

He stressed that an appeal judge is justified in intervening with the sentence of a district court only where the decision was wrong, or the district judge had erred in assessing the material before him, erred in principle in making the sentence or imposed an excessive or inadequate sentence.