Now we know why the Government is planning to spend £4 billion on new prisons.
It's not, as I suggested in my previous post, because ministers want to cut overcrowding or close outdated jails, both of which would be laudable aims.
It's simply because, without a dramatic increase in capacity, they will run out of room for prisoners.
That has become clear thanks to the latest prison population projections for England and Wales. Published today by the Ministry of Justice (MoJ), they make for startling reading.
The jail population, which is currently less than 79,000, is forecast to rise by 20,000 in six years. Yes, 20,000 in six years.
Even by the standards of Britain's post-war love affair with incarceration that is a huge increase in a comparatively short period of time.
And while there are many people who would welcome a tougher approach to sentencing, with more offenders being locked up, there aren't enough cells to accommodate a rise on that scale.
According to the MoJ, "useable operational capacity", in other words, the number of places available in prisons, is currently around 81,400. But the prison population is projected to grow to over 88,000 in just two years before climbing to 98,700 by September 2026. There are other "scenarios", set out by MoJ statisticians, under which the population rises even faster and further, hitting 100,000 in 2025.
The projected increase is partly down to sentencing changes which will result in longer jail terms for serious offenders.
But the main reason, according to the MoJ, is the expected surge in the number of police due to the Government's well-publicised campaign to hire an extra 20,000 officers by 2023. Individual forces also have their own, separate, recruitment initiatives which will add a further 3,400 to the total.
It was always anticipated that a rise in police officer numbers would lead to an increase in arrests, charges and convictions, resulting in more people being jailed, but this is the first time the effect has been publicly quantified.
Yesterday, the Chancellor said the Government's prison building plans would provide an additional 18,000 places, around 4,500 more than previously announced. But it takes a long time for places to come on stream - either in new jails or at existing sites.
Only three new prisons have been confirmed: HMP Five Wells is due to open in Northamptonshire next year; in 2022, a new prison at Glen Parva, Leicestershire, will be completed; and by 2024, a facility near Full Sutton, Yorkshire, is due to open. The new establishments will add around 5,000 to total capacity. There are other proposals, to construct new house-blocks at existing prison locations, but capacity will still be far short of the projected population. If the estimates are even broadly accurate, the Government will be short of cells within a few years. In 2024, the population is forecast to hit 96,000 - yet there will be only around 87,000 places, on the basis of the current, published plans.
The projections, of course, may turn out to be incorrect; they've not always been reliable in the past and predicting the prison population is notoriously difficult - who would ever have thought 12 months ago that it would fall by 5,000, as it has done, largely because of the pandemic?
Or, perhaps the Ministry of Justice has something up its sleeve. After all, ministers have said they want to build three other prisons - in north-west and south-east England.
But the locations have yet to be identified. Planning permission will have to be sought and agreed; contracts awarded; sites cleared. It will take many years.
And the clock is ticking.
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