THREE men who wore T-shirts depicting a kangaroo dressed in judge's robes were sentenced to jail for contempt of court on Thursday, after they refused to apologise for their actions.

Singapore Democratic Party (SDP) assistant secretary-general John Tan Liang Joo, 47, was sentenced to 15 days in jail.

Activist Isrizal Mohamed Isa, 33, and full-time national serviceman Muhammad Shafi'ie Syahmi Sariman, 20, were each sentenced to seven days in jail.

Justice Judith Prakash also ordered each of them to pay $5,000 in costs to the Attorney-General's Chambers, as well as other expenses it incurred during the proceedings.

But the trio are not starting their jail terms immediately.

Justice Prakash gave time for Isrizal to settle his personal affairs and Shafi'ie to complete his basic military training.

They are to surrender themselves on Dec 12.

Tan, who told the court he is considering an appeal, was given until Dec 18, after he said he was considering an appeal to start serving his jail term.

In sentending the three, Justice Prakash - who found the trio in contempt of court at a hearing on Monday - noted that they did not apologise and withdraw the insinuations they made about the courts when they were given the opportunity to do so.

'The fact that none of you have shown any contrition, but maintained what you did was justified and fair criticism when it was not fair criticism - and I will explain in my judgement why it was not fair criticism - I think there is no alternative in this case but to impose a sentence of incarceration,' she said.

Her decision came after a one-day hearing on Monday.

The Attorney-General's Chambers initiated contempt of court proceedings against the men for having 'scandalised the Singapore Judiciary by publicly wearing identical white T-shirts, imprinted with a palm-sized picture of a kangaroo dressed in a judge's gown, within and in the vicinity of the New Supreme Court Building'.

They wore the T-shirts between May 26 and May 28 at the Supreme Court.

This was when they were at hearings where Justice Belinda Ang assessed defamation damages that the SDP, its leader Chee Soon Juan and his sister Chee Siok Chin had to pay Prime Minister Lee Hsien Loong and Minister Mentor Lee Kuan Yew.

On Monday, Deputy Solicitor-General Jeffrey Chan sought a stiff jail terms for the trio, saying that the worst insult someone can level against the judicial system is to call it a kangaroo court.

This is generally understood to mean a court that is characterised by unauthorised or irregular procedures, or sham and unfair legal proceedings.

Mr Chan said the men's refusal to apologise reaffirmed their contempt of court. He urged Justice Prakash to pass a sentence that would denounce such a show of contempt and deter others from acting in the same way.