What is now known is that expert projections on future prisoner numbers - first made some 20 years ago by two separate consultants, then revised and revised again - were not heeded.

This has now culminated in a massive management headache for ACT Corrections which struggles - because of the jail's small footprint - to properly keep detainee cohorts apart.

The original plan for the Alexander Maconochie Centre was to separate prisoners on remand - that is, those who have been refused bail, have their case still before the courts, or are awaiting sentence - from those convicted.

Remandees are the most unsettled and unstable cohort within any prison system. Remand prisoners have higher rates of drug and mental health issues, regularly experience frustration and uncertainty and are more likely to be disruptive in their behaviour.

Back in 2001, the ACT's prisoner population was just 160. Some were held in the Belconnen Remand Centre and others in the old Periodic Detection Centre in Symonston but most were incarcerated within the NSW system - males mostly in Junee and Goulburn, and females at Mulawa and Silverwater - which was an onerous trip for ACT families wanting to visit.

Two separate consultants were engaged to predict the population of the Canberra prison in 2018. One said 445 while another went further, saying the facility should accommodate 480 prisoners with potential growth to 600.

FOI documents revealed the ACT Treasury railed against both projections, claiming this threatened the financial viability of the project. Treasury officials, assuming a greater knowledge than the experts, even claimed "imprisonment rates of this [high] level may be contrary to the innovative and restorative justice principles promoted as underpinning the philosophy of the proposed prison".

In 2006, Treasury recommending the deletion of the Transitional Release Centre completely, scrapping a 10-bed women's remand cottage and stopping the gym fit-out.

As former Attorney-General Simon Corbell admitted to the ACT Legislative Assembly: "Yes, we are delivering fewer [prison] beds than we anticipated." He blamed high construction costs.

Mr Corbell said the government, committed to the project, "had two choices: one was to reduce the scale of the project, the other was to increase the [financial] appropriation". The government chose the former.

Mr Corbell further added: "The advice I have is that it gives us the [bed] capacity, certainly for the next 20 to 25 years."

How wrong that advice proved to be.

Overcrowding is now a fundamental issue. The prison now regularly has over 500 inmates, with more than a third on remand.

Of equal concern is detainee boredom. In a survey of the detainees two years ago, 63.8 per cent agreed they were bored "most of the time", and 22 per cent "sometimes" because there were not enough productive things to do.

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