The Court of Appeal yesterday ruled that the ongoing detention of opposition leader Kem Sokha was legal, despite claims his parliamentary immunity had been violated – and in spite of the fact that neither the accused nor his representatives were present.

Defence lawyers for the jailed Cambodia National Rescue Party president – who stands accused of “treason” – walked out of the courtroom in protest after the court refused to allow Sokha to attend the hearing. Nonetheless, the hearing proceeded, with court spokesman Touch Tharith saying a judge had ruled Sokha’s continued imprisonment was legal.

“This morning the judge of the Appeal Court decided that the decision of the investigating judge to put the accused Kem Sokha in pretrial detention is correct,” he said.

In a statement released later, Tharith called the lawyers’ decision to walk out “regretful” and asserted that a hearing related to procedure did not require the presence of the accused. “The law allows letting the court consider and proceed with the absence of the accused,” he said.

According to Sam Sokong, one of Sokha’s eight lawyers, the defence first requested the court to delay the hearing. When that request was rebuffed, the group walked out. Sokha was arrested earlier this month and charged with “treason” based on a 2013 video in which he talks about having received advice from the United States on political strategy. His lawyers challenged the legality of his arrest, noting that he enjoyed constitutionally mandated parliamentary immunity, and arguing that it was illegal to arrest him after midnight for anything other than an in flagrante delicto – or “red-handed” – offence.

Authorities, however, have rejected this reasoning, claiming the purported crime was indeed a flagrant offence, allowing officers to arrest him at any time – and in spite of his immunity.

The government, however, has frequently been accused of violating the constitutional immunity of lawmakers, and despite lacking the two-thirds majority required to approve the prosecution of a lawmaker, ruling Cambodian People’s Party parliamentarians have voted to allow Sokha’s case to proceed.

Sokong yesterday called the judge’s decision to hold the hearing without Sokha present a violation of his rights. “The accused has the right to provide evidence and answer questions [in person]. If the accused is not in the courtroom, it means the hearing is meaningless,” he said. “The court decided to detain the accused in order to [make him] appear in court, so why did they not bring him to the court now?” he asked.

The defence team travelled to Tbong Khmum province’s Correctional Centre 3 to meet with Sokha, but could not provide details of what was discussed.

Legal expert Sok Sam Oeun said the decision to keep Sokha from the hearing breached international human rights law and the Constitution.

“[Cambodia] recognises the [International Covenant on Civil and Political Rights] and all relevant international law, as recognised by the Cambodian Constitution. And the right of the accused to appear is stated in the ICCPR,” he said.

CNRP Deputy President Mu Sochua, who gathered outside the court with other opposition lawmakers, called the process a “mock trial”.

“Mr Kem Sokha’s rights were being totally violated, so it comes to what we’ve been saying all along,” she said. “This is a political case with the goal to give the ruling party the upper hand with regards to the next elections. It’s not a level playing field.”

The CNRP’s response to Sokha’s arrest has been measured, with no demonstrations called for by the party. In perhaps its most visible act of dissent since the arrest, the party on Monday began putting up banners throughout the country calling for Sokha’s unconditional release, which the government quickly ordered removed.

Interior Ministry spokesperson Khieu Sopheak was quoted in local media as saying that the banners linked the CNRP to the “treasonous activities” of Sokha, which he said could lead to the dissolution of the party.

Controversial new changes to the Law on Political Parties – first designed to sideline Sokha’s predecessor, Sam Rainsy – do allow for the dissolution of parties “conspiring” with convicted criminals. Sokha, however, has not been convicted, and under the Constitution is presumed innocent until proven guilty.

Sopheak could not be reached yesterday, but was reported as saying that the ministry would wait to see if the CNRP would take the banners down. If they do not, he said, the authorities would remove them.

Touch Sa Im, the head of the CNRP executive committee in Kampong Speu province, confirmed that the Chbar Mon town governor came to the Kampong Speu CNRP office yesterday morning and told him to take down the banner.

“But I told him that we won’t do that right now, because across the country they have not done that. Now, they just came to tell us to do so, but I don’t know what will happen next,” he said.

Kem Monovithya, the deputy CNRP public affairs officer and daughter of Sokha, said the party would not take the banners down. “They can come to take it down, just as they raided Kem Sokha’s house after midnight and handcuffed [him] without a warrant,” she said.

Deputy President Sochua, meanwhile, said the government needed to present clear legal basis before ordering them to remove the signs. “They need to tell us first which law we have broken,” she said.

Amid the tense political climate, the CNRP has seen at least a dozen of its lawmakers leave the country, which the party has maintained is unrelated to political pressure. Fellow Deputy President Eng Chhay Eang, who is currently abroad, said yesterday that he would be back in October.