Former prosecutor Spencer Gwee Hak Theng was sentenced by a district court on Friday to four months in jail for having sex with an underage prostitute.

Standing in the dock, the 60-year-old lawyer displayed no emotion. He had been convicted last week of having paid a 16-year-old Vietnamese prostitute $300 for sex at the Four Chain View Hotel in Geylang on the evening of July 19, 2011. He is appealing against both conviction and sentence and was freed on bail of $20,000.

His lawyer, Mr Subhas Anandan, told reporters after the hearing that he had advised Gwee to appeal on grounds of law as well as on the facts of the case. Gwee denies having sex with the Vietnamese teen.

During the 10-day trial, he said that he had been discussing business with a client at a Geylang coffee shop around the time the offence occurred.

The client, engineer Arthur Chew, had testified that he was with Gwee on the night of July 19 until about 11.50pm - yet hotel records showed Gwee had checked in at 11.41pm.

Mr Chew's testimony was further contradicted by "objective, independent evidence" from three hotel employees that placed Gwee at the hotel at the time of the offence.

The question of law that the defence team would be bringing up at the appeal is that even if Gwee had sex with the teen, he could not have known she was underage as she had told him she was 19 years old.

The date of the appeal hearing has yet to be announced.