We may run out of prison space despite building more - minister

As part of the government's strategy, it is also changing planning rules relating to building prisons.

It said prisons would be deemed sites of "national importance", placing the power to green-light planning applications solely in ministers' hands, and with decisions to take no longer than 16 weeks.

The government said £2.3bn had already been secured through the Budget to pay to build the four new prisons, until 2026.

Another £500m will be spent on prison maintenance and the probation service across the next two years.

But His Majesty's Prison and Probation Service estimates it would cost £2.8bn over the next five years to bring the whole estate into a fair condition, more than double its current maintenance expenditure.

And the National Audit Office warned last week that prison expansion costs were expected to be at least £4.2bn above original estimates in 2021.

As well as this prisons strategy, the government hopes a separate review into sentencing could be a longer-term solution to reduce demand on prisons.

The review of prison sentences is being led by David Gauke, a former Conservative justice secretary.

The review is expected to consider scrapping short sentences and toughening up community orders as an alternative to jail. It will report back next spring.

Asked by the Today programme whether some people currently in prison might not be in the future, Mahmood said it was a possibility.

"Yes... We will have to expand the range of punishment available outside of prison, that does mean that we will have more offenders monitored outside," she said.

"But I want to make sure that when we are not putting someone in prison but they're being punished outside, that that is still a punishment they can have confidence in."

The Conservative government had pledged to build 20,000 new prison places by 2026.

HMP Prison and Probation Service had created more than 6,518 as of September.

The Labour government has pledged to create the remainder - about 14,000 - by 2031, a promise already made during the election campaign

Last week, the National Audit Office released a critical report saying that Boris Johnson's government pledge to create an extra 20,000 cell spaces was now not expected to be met until 2031 – about five years later than promised. It also said the scheme was running £4.2bn over budget.

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