An assistant service engineer, who had unprotected sex with his 15-year-old stepdaughter in a car after he picked her up from school, was sentenced yesterday to three years' jail.

The 41-year-old Singaporean pleaded guilty last month to one count of having sex with the underage girl.

According to court documents, he committed the offence "with her consent". A second similar charge was taken into consideration during sentencing.

The man cannot be named as a gag order has been imposed to protect the girl's identity. The Straits Times understands he is still married to her mother, and the girl referred to him as "uncle".

Deputy Public Prosecutor Derek Ee had earlier told District Judge Teo Guan Kee: "The accused stated that he initially treated the victim as his stepdaughter. However, as time went by, they gradually became closer and often texted each other.

"This eventually led to the accused having sex with the victim."

The man picked up the Secondary 4 student from school at around 12.30pm on Jan 25 this year.

Instead of going home, he drove to a multi-storey carpark in Admiralty Drive. The pair moved to the rear passenger seat and the man had unprotected sex with the teenager.

A police officer was in the vicinity at around 2pm when he spotted them. When they saw the policeman, they quickly dressed themselves.

The man initially denied having sex in the car when questioned, the court heard. Upon further investigation, they later admitted it.

Yesterday, DPP Yan Jiakang told the court that the man had abused the trust placed in him and urged Judge Teo to sentence him to three years' jail.

Defence lawyer Dilip Kumar pleaded for his client to be sentenced to a year's jail or less. He told Judge Teo that the man was remorseful and "understands that what he did was very wrong".

The man married the girl's mother in 2016 and they have between them 10 children - ranging in age from two to 24 - mostly from previous marriages, added the defence lawyer.

The man was offered bail of $25,000 and ordered to surrender himself to the State Courts on Jan 3 to begin serving his sentence.