The Court of Appeal yesterday cut a robber-rapist's jail term by two years, despite its view that his original sentence of 17 years' jail and 24 strokes of the cane "befits the heinous nature of his crimes".

The three-judge court allowed the appeal because the jail term handed down to Chang Kar Meng, 29, in 2015 was out of line with precedent in comparable cases.

However, the court made it clear that after Chang's case, those convicted of robbery and rape should not expect to benefit from similar leniency.

The court said that it disapproved of several of the precedent sentences for being too lenient or based on the wrong legal principles, after examining the six cases of rape and robbery.

But the court said that it had to be fair to Chang, because at the time of his sentencing he had harboured a legitimate expectation of a sentence that was based on these precedents. The sentence of caning remains unchanged.

Chief Justice Sundaresh Menon, delivering the court's decision, said: "Although we are of the view that the sentences meted out in several of these precedents were inadequate and/or premised on errors of law, nonetheless, in fairness to the appellant, the sentencing approach which we set out in this judgment for cases of rape and robbery will only take effect prospectively and will not apply to him."

In March 2013, Chang, then a kitchen worker, decided to rob a woman he spotted in Paya Lebar walking home from work.

He sneaked up behind the 33-year-old waitress as she waited for the lift and knocked her senseless with a neck chop. Chang dragged her aside and took her phone, sling bag and jewellery.

He then took her to a grass patch nearby, where he took photographs of her exposed breasts, fondled her and raped her.

During the rape, the woman came to but pretended to remain unconscious out of fear. He then took more photos and dressed her.

Chang put her work permit, prayer card and house key in her pocket before walking away with her bag. She was about to flee but he returned, so she lay back down on the grass. He then carried her to a staircase landing, laid her on a mattress and took a photo of her.

His DNA was found on the woman's body and clothes and he was arrested 5½ months later at the rental flat that he shared with his girlfriend.

Chang, represented by Mr Sunil Sudheesan, pleaded guilty to one charge each of rape and robbery.