Prime Minister Sir Keir Starmer has said overcrowding in prisons in England and Wales is “worse than I thought it was” and the previous Conservative government was “reckless” to allow such a situation to take hold.

His comments come as the government has said it will announce its plans for releasing some prisoners early on Friday.

Non-violent prisoners could reportedly be released to free capacity after serving 40% of their sentences, instead of the current policy of waiting until they have served half.

The former Justice Secretary Alex Chalk said there needs to be a debate about how many people the government can afford to lock up.

Last week the Prison Governors’ Association, which represents 95% of prison governors in England and Wales, warned that jails were due to run out of space within days.

Now, Sir Keir has said he was “pretty shocked” to discover the scale of the situation.

During the election campaign, he said a Labour government would “in all likelihood” have to continue the early release of prisoners due to overcrowding in jails.

Speaking to the The Today Podcast, Alex Chalk, who was justice secretary until just last week, when his party lost power in the general election, said releasing prisoners early would buy the government “18 months” but added: “It won’t buy you any more than that”.

He said the new Justice Secretary Shabana Mahmood would have to be “very frank and credible about the long term”.

“If the situation is that we haven’t got new money, are you seriously going to be saying that instead of building a new hospital, we’re going to be building a new nick at the cost of £600,000 per cell?”

In March, Mr Chalk announced plans to release prisoners up to two months early in a bid to ease overcrowding.

The Ministry of Justice is building six new prisons to create an extra 20,000 spaces.

Labour has not yet set out what it will do, but Sir Keir’s appointment of James Timpson as prisons minister suggests he will pursue a change of approach.

Mr Timpson, the boss of the shoe repair chain which has a policy of recruiting ex-offenders, said in an interview with Channel 4 earlier this year that “we’re addicted to punishment” and that only a third of prisoners should be there.

Sir Keir is currently in Washington DC to attend a Nato Summit. On the plane to the US, he was asked by reporters what he had discovered about the state of public spending now he’s in office.

Sir Keir replied: “Some of what we’ve found is shocking, not so much about the finances, but I have to say, on prisons”.

“The situation is worse than I thought it was. I’m pretty shocked that it’s been allowed to get into that situation. It’s reckless to allow them to get into that place.”