A 55-YEAR-OLD man who sexually assaulted his teenage daughter over a period of four years will now be spending 24 years in prison, after an appeal by the prosecution.

In increasing the man's jail term from 16 years, the three-judge Court of Appeal, headed by the Chief Justice, said that the courts will punish serious sexual offenders severely.

'Rape is one of the most serious offences in the statutes, more so in this case when it is perpetrated by a father against his biological daughter of a tender age,' said CJ Chan Chan Sek Keong.

He agreed with prosecutors that the original eight-year jail term handed down by the High Court was too light.

'The sentence must reflect the abhorrent nature with which this kind of offence is viewed in our society,' he said.

The man, a former part-time security guard, began sexually abusing his daughter at home when she was 10. The rapes started when she was 12. He crept into her room and violated her on the double-decker bed she shared with her younger sister.

The mother of the two girls was the man's mistress. The family lived in a four-room HDB flat. The man had a wife and son who lived elsewhere.

The repeated sexual assaults, which began in 2002, came to light in Dec 2006. During a quarrel with an aunt, the girl retorted that she did not like the love that her father gave her.

The details then spilled out: her father had sex with her 'once to twice a month' and never used a condom.

In August last year, the man pleaded guilty to three counts of aggravated rape. Justice Choo Han Teck handed down the minimum sentence - eight years on each count, with two of the terms to run consecutively.

The man escaped caning due to his age. Two aggravated rape and five molestation charges were taken into consideration.

The trial judge noted that the victim and her family had written letters asking for leniency as they had forgiven the man.

At the appeal on Tuesday, Deputy Public Prosecutor Daniel Koh argued that there was no basis to let the accused off with the lightest possible sentence.

Citing a slew of precedent cases, the DPP noted that the appropriate sentence for rape perpetrated by a father against his daughter should be between 12 to 18 years' jail for each charge.

A sentence of eight years is unprecedented, he said. The DPP argued that the trial judge had put too much weight on the fact that the victim and her family had forgiven the man.

The girl may have written the letters in the misguided hope of keeping the family intact or may have been pressured by other family members to do so, the DPP argued.

The man, who was not represented by a lawyer, told the court on Tuesday that he would have to live with the pain and shame for the rest of his life.

He pleaded with the judges to let him spend his twilight years with his family, to make amends to them.