The Northern Territory government refused to release CCTV vision from a major disturbance at the notorious Don Dale juvenile detention centre under freedom-of-information laws.

Guardian Australia revealed earlier this week that the NT was the worst-performing jurisdiction in the country on FOI. The territory government refused about 27% of all FOI requests it received last financial year, a rate seven times higher than Victoria and eight times higher than Western Australia.

The NT opposition used FOI to attempt to secure footage of a disturbance in November, when two inmates attacked a guard and released other detainees from their cells. The school’s facility was set on fire and destroyed and inmates used angle grinders to cut fences and try to escape.

The opposition’s FOI request asked for videos or pictures of the incident, including “moving pictures, closed circuit television transmissions, still pictures, photographs, videos, computer files, electronic mail attachments, mobile phone files, and multimedia texts”.

Vision from inside the Don Dale centre, showing separate incidents, has proved hugely important to the public interest in the past. Footage showing the mistreatment of detainees at Don Dale sparked a royal commission into juvenile justice, which found “shocking and systemic failures” that were ignored at the highest levels of government.

The recent FOI request was rejected by the territory government last month. The government argued the vision would “prejudice the maintenance of law and order in the territory” because the vision would interfere with a current police investigation and may be used “as evidence in an upcoming court hearing”. The NT’s information act does contain exemptions to FOI designed to preserve the justice system, including to “prejudice the prosecution of an offence”.

But the opposition argues the eight detainees involved in the disturbance have already been charged, and so little impact is likely on the police investigation.

The NT government said the footage also “identifies numerous third parties”, posing a privacy risk. But the opposition said their identities could have been protected by the blurring of faces, a practice often used when privacy concerns arise.

The NT opposition leader, Gary Higgins, said the reasons were “frivolous” and did not “hold water”.

“Labor spruiks endlessly about providing an open and accountable government but their pledges of transparency is a tissue of lies – they clearly have a lot to hide,” he said.

The NT chief minister, Michael Gunner, said the opposition’s comments were “completely irresponsible” and risked interfering with the ongoing court case.

“It is completely irresponsible for Gary Higgins to actively interfere with this court process for political purposes,” Gunner said.

“For Gary Higgins to publicly criticise his FOI refusal shows his complete lack of understanding of basic court procedures and a blatant disrespect to our hardworking police officers and this investigation.”

Labor came to power in 2016 pledging to improve accountability and integrity measures. It has acted on numerous fronts, including the setting up of an integrity commission, better disclosure of political donations and the registrable interests of MPs.

The NT has had a consistently high refusal rate for FOI requests. In 2016-17, it refused 28% of FOI requests, by far the highest rate in the country, and eight percentage points higher than the next highest jurisdiction, Queensland.

The territory’s refusal rate has been above 20% for four years running. There are often legitimate reasons for denying an FOI request, including that the documents do not exist or are lawfully exempt from release.