The Court of Appeal on Thursday slashed four years off the jail term handed down to a 28-year-old former auxiliary police officer who had arranged for another man to have sex with his girlfriend during bondage sex, without her consent.

Reducing the jail term from 23 years and 11 months to 19 years and 11 months, the court agreed with his lawyers that the original sentence was "crushing" for someone who was relatively young and had a clean record until the offences.

The man, who cannot be named to protect the woman's identity, pleaded guilty last year to two charges of abetment of rape and one charge of abetment of sexual assault by penetration.

He was sentenced to 23 years and 11 months' jail and 24 strokes of the cane.

At his appeal on Thursday, the man, represented by Mr Ramesh Tiwary and Ms Diana Ngiam, argued that the sentence was significantly above that for rape offences.

Mr Tiwary said the trial judge had not calibrated the individual sentences for each charge to ensure that the combined sentence was not manifestly excessive.

He said the man had offered to testify against the co-accused and pleaded guilty to spare the victim the trauma of testifying in court.

Deputy Public Prosecutor Winston Man said the man was not as cooperative as portrayed, noting he pleaded guilty only last November but the offences took place in 2016.

The court, comprising Judge of Appeal Judith Prakash and Justices Chao Hick Tin and Woo Bih Li, cited the totality principle in reducing the jail and caning sentences for each charge, making a final sentence of 19 years and 11 months.

The man had cajoled his girlfriend to engage in bondage sex but she refused when he suggested that a third person join them for sex.

He then hatched a plan for a threesome - without her knowledge - with 23-year-old Srihari Mahendran, whom he had met online.

On April 29, 2016, he tied her hands, blindfolded her and let Srihari into the hotel room. He had sex with her before Srihari took over.

In August 2016, the woman arranged a staycation to celebrate the man's birthday and he had Srihari join them. The woman realised something was amiss when she felt two people touching her. She removed her blindfold and saw Srihari.

Both men were arrested at the hotel. Srihari's trial is expected to take place in November.