The scale of the challenge facing Prime Minister Keir Starmer's new government is writ large in Britain's prisons, which are within weeks of being too full to accept new inmates, leaving the government with unpalatable and costly choices.

Britain has western Europe's highest rate of incarceration, according to the World Prison Brief database and faces a crisis after a new building programme failed to keep track with tougher sentencing laws that have fuelled a growing prison population.

Already many prisons are housing two inmates in cells built for one, and emergency measures triggered by the previous Conservative government mean some offenders have been released early and court cases delayed to avoid new arrivals.

The head of the body representing prison governors has warned that unless a solution can be found, offenders will soon have to be held in police cells - constraining officers and disrupting the wider judicial system.

Labour leader Starmer has described the state of Britain's prisons as a "monumental failure" of the last government, but like other challenges - from sewage in rivers to strikes at the National Health Service - that stance may only hold for so long.

He also has little financial room to manoeuvre. According to the Institute for Government (IfG) think tank, spending on prisons is set to fall by 5.9% each year relative to demand over the coming years.

Tom Wheatley, president of the Prison Governors Association, said the new government had no time to waste.

"I think they can (act quickly enough), but only just. It's going to be touch and go," he told Reuters.

"We're nearing the line on what can be safely accommodated, even in overcrowded conditions."