The ongoing inquiry into Serco's management of Mount Eden Prison is being used to withhold official reports about incidents at the facility.

Newstalk ZB had requested a copy of the special monitor's report on fight club allegations, official reports on prisoner on staff and prisoner versus prisoner assaults at the prison.

However, the Corrections Department is declining to release any details while an investigation into the prison by the Chief Inspector is underway.

It said to do so could prejudice that investigation and any related police inquiries.

The Department's also declining to release reports on 115 security incidents that occurred at Mount Eden Prison in the last financial year.

Details released under the Official Information Act by the Corrections Department reveal Serco has faced contract deductions in each of the last four financial years. Those were all for failing to properly notify incidents that have occurred within the jail.

In total, a $250,000 worth of deductions have been made from Serco's contract because of the breaches. They're part of $1.4 million worth of deductions Serco has had imposed on it since it took over the running of the prison, because of its contractual failures.

Labour MP Jacinda Ardern said one of her party's main concerns is Serco's had a different level of transparency applied to it.

"There's just certain information that we cannot get out of Serco. That shouldn't be the case, I think there should be even greater transparency. I would say that should apply where there is a particular public interest in incidents that have been inquired into."

"If we know that the failure to provide information is one of the things they've been penalised for, there could be a raft of other areas where they would have been penalised had that information have been available."

Details of contraband incidents reported at the facility in the last financial year have also been released.

In total there were 762, with over 200 being either drug or alcohol related - 79 incidents of homebrew substances were reported as were 43 cases of cannabis use.

62 weapon related incidents were also recorded, 41 of them involving improvised weapons.

However, The Minister of Corrections is standing by his department's decision not to release reports relating to Serco's management of Mount Eden Prison.

Sam Lotu-Iiga said it's right and proper that the special monitor's report be withheld, given it was incomplete and a draft only.

He said the Chief Inspector's review, due later this month, will supersede that report.