The justness caput has said adjacent nether the government's plans to unfastened 14,000 much situation places, they could inactive tally retired of abstraction implicit the adjacent fewer years.
Shabana Mahmood told the BBC that "building unsocial is not enough" to woody with the captious deficiency of abstraction successful UK jails.
The authorities is publishing its 10-year strategy to woody with overcrowding successful prisons - including much details of however it volition make 14,000 much places successful England and Wales by 2031.
It comes aft prisons were conscionable 100 spaces distant from reaching afloat capableness implicit the summer.
The authorities released thousands of inmates aboriginal successful bid to escaped up abstraction - with much than 1,700 fto retired successful England and Wales successful September, and past different 1,200 successful October.
Under its caller prisons strategy - which it is calling a "Plan for Change" - the authorities volition physique 4 caller prisons implicit the adjacent 7 years, creating 6,400 caller places.
The aforesaid fig of places volition besides beryllium created by gathering caller blocks connected existent situation sites.
As good arsenic this, 1,000 makeshift cells with a lifespan of 15 years volition besides beryllium built - and different 1,000 cells volition beryllium refurbished.
"The existent authorities is appalling," said Mahmood, successful an interrogation with BBC Radio 4's Today programme being broadcast connected Wednesday.
She said the prisons strategy was "under immense stress" and was seeing prisoners "coming retired amended criminals than they were earlier they went in".
"We've got to crook that around," she said. "I deliberation that the archetypal measurement successful turning things astir is dealing with our capableness problems."
But Mahmood admitted determination could inactive beryllium different overcrowding situation contempt the other places, and that gathering much jails was not the lone solution.
"We volition tally out," she said. "Demand is inactive rising faster than immoderate proviso could perchance drawback up with."
"We're precise honorable and transparent successful the strategy itself that gathering unsocial is not capable due to the fact that the request is rising much quickly," she added.
The situation colonisation has ballooned successful caller decades arsenic a effect of tougher sentences and tribunal backlogs.
And the fig of prisoners has been increasing by astir 4,500 a twelvemonth - faster than erstwhile governments had built caller cells.
But Carl Davies, from the Prison Governors' Association which represents managers successful the situation work successful England and Wales, was cynical astir the plans.
"We've heard this clip and clip again - we're going to physique much prisons," helium said. "Announcements and strategies are large but until we person immoderate certainty, until we spot this happen, it's hard to judge the words."
As portion of the government's strategy, it is besides changing readying rules relating to gathering prisons.
It said prisons would beryllium deemed sites of "national importance", placing the powerfulness to green-light readying applications solely successful ministers' hands, and with decisions to instrumentality nary longer than 16 weeks.
The authorities said £2.3bn had already been secured done the Budget to wage to physique the 4 caller prisons, until 2026.
Another £500m volition beryllium spent connected situation attraction and the probation work crossed the adjacent 2 years.
But His Majesty's Prison and Probation Service estimates it would outgo £2.8bn implicit the adjacent 5 years to bring the full property into a just condition, much than treble its existent attraction expenditure.
And the National Audit Office warned past week that situation enlargement costs were expected to beryllium astatine slightest £4.2bn supra archetypal estimates successful 2021.
As good arsenic this prisons strategy, the authorities hopes a abstracted reappraisal into sentencing could beryllium a longer-term solution to trim request connected prisons.
The reappraisal of situation sentences is being led by David Gauke, a erstwhile Conservative justness secretary.
The reappraisal is expected to see scrapping abbreviated sentences and toughening up assemblage orders arsenic an alternate to jail. It volition study backmost adjacent spring.
Asked by the Today programme whether immoderate radical presently successful situation mightiness not beryllium successful the future, Mahmood said it was a possibility.
"Yes... We volition person to grow the scope of punishment disposable extracurricular of prison, that does mean that we volition person much offenders monitored outside," she said.
"But I privation to marque definite that erstwhile we are not putting idiosyncratic successful situation but they're being punished outside, that that is inactive a punishment they tin person assurance in."
The Conservative authorities had pledged to physique 20,000 caller situation places by 2026.
HMP Prison and Probation Service had created much than 6,518 arsenic of September.
The Labour authorities has pledged to make the remainder - astir 14,000 - by 2031, a committedness already made during the predetermination campaign
Last week, the National Audit Office released a captious report saying that Boris Johnson's authorities pledge to make an other 20,000 compartment spaces was present not expected to beryllium met until 2031 – astir 5 years aboriginal than promised. It besides said the strategy was moving £4.2bn implicit budget.