LONDON (Reuters) - British Prime Minister Keir Starmer's new government will widen the early release of prisoners to tackle an overcrowding crisis that has left jails within weeks of running out of space, prison governors said on Thursday.

Britain's Prison Governors' Association said in a statement to media that it had been "reliably informed" that rules would change on Friday so that most inmates would serve only 40% of their sentences behind bars, down from a typical 50% at present.

Prisoners who are released are meant to be supervised by probation officers, and can be returned to jail if they reoffend or break other terms of their release.

"The changes to release dates will create essential space across the prison system," the Prison Governors' Association said in a statement.

Britain's Ministry of Justice, which oversees prisons, had no immediate comment.

Starmer told reporters on a trip to Washington on Wednesday that the government would soon make a statement on prison overcrowding and criticised former Prime Minister Rishi Sunak's government for being reckless in its approach to the issue.

Britain has western Europe's highest rate of incarceration - more than twice that in Germany or the Netherlands - although the figure is only around a quarter of the U.S rate.

Starmer's Labour won a landslide election victory last week to return to power for the first time since 2010.

One of Starmer's eye-catching initial moves was to appoint businessman James Timpson as prisons minister. Timpson's shoe-repair and key-cutting firm employs ex-offenders and he is known for his belief in rehabilitation.

The prison governors said overcrowding had worsened under the previous Conservative administration, which lengthened some jail terms and increased the percentage of sentences which more serious violent and sexual offenders must serve behind bars.

Construction delays and a lack of maintenance meant prison capacity did not keep up. Inmates near the end of their sentences were released at short notice on an unplanned basis, which can increase the risk of reoffending or homelessness.

"We are hopeful that the penal populism agenda will become a thing of the past and that this new government will be willing to invest in our service," the Prison Governors' Association said.

Existing plans show prisons are likely to face reduced budgets in the coming years.

(Reporting by David Milliken and Elizabeth Piper)

By David Milliken and Elizabeth Piper