More than 100,000 prisoners could be held in jails in England and Wales within five years, according to government estimates.
The prison population is projected to increase to between 95,700 and 105,200 by March 2029, with a central estimate of 100,800, figures published on Thursday show.
The Ministry of Justice (MoJ) said the potential rise is driven by factors including “continued growth” in suspects being charged and prosecuted, more cases coming to court, the “rising levels of people on remand” and “changes in sentencing policy and behaviour to keep the most serious offenders in prison for longer”.
It comes after Whitehall’s spending watchdog warned earlier this week that Government plans to boost prison capacity could fall short by thousands of cell spaces within two years and cost the taxpayer billions of pounds more than anticipated.
Since September the Government has been freeing thousands of inmates early in a bid to cut jail overcrowding by temporarily reducing the proportion of sentences which some prisoners must serve behind bars in England and Wales from 50% to 40%.
But prisons are still expected to reach critical capacity again by July.
MoJ figures show there were 86,059 adult prisoners behind bars in England and Wales on Monday, slightly higher than the 86,038 recorded at the beginning of last week.
The so-called operational capacity for English and Welsh men and women’s prisons is 88,852, indicating there is now cell space for 2,793 criminals.
An additional 1,350 cell spaces tend to always be kept free above the overall operational capacity of the prison estate in England and Wales as a contingency measure so jails can cope with a sudden influx of inmates or change in the make-up of the prison population, according to the MoJ.
The latest data means the prison population is only 2.8% lower than when the number of inmates being held hit a record high of 88,521 on September 6, PA news agency analysis shows.
The new peak is the highest end-of-week figure since weekly population data was first published in 2011.
It is also higher than the average annual prison population in every year since modern records began in 1900.
The MoJ report indicated the prison population is now estimated to be 5,500 lower by September 2028 than previously projected in light of measures like the early release scheme being taken.
In a report published on Wednesday, the National Audit Office (NAO) said current expansion plans are “insufficient to meet future demand” amid a projected shortage of prison places by the end of 2027, with costs expected to be at least £4 billion higher than initially estimated.
The prisons overcrowding crisis is down to the failure by the previous Conservative government to make sure policy changes bringing in longer jail sentences and boosting police numbers matched the space available in prisons to hold criminals, according to the findings.
Prisons minister Lord Timpson said: “These new projections reveal that, unless we act now, our prisons will return to crisis.
“We’ve already taken immediate action to stop the imminent collapse of our prisons. We are now setting out our plans so no government inherits the situation we did.
“We will build the 14,000 prison places the last government promised but did not deliver, and have commissioned an independent review of sentencing to ensure we can always lock up dangerous offenders and never run out of prison places again.”
