Young adults in jail are among the worst affected by Britain's prison overcrowding crisis, campaigners have claimed.
The YMCA warned that offenders aged between 18 and 25 were "particularly vulnerable" because they received little help to turn away from a life of crime.
The organisation warned that a shortage of prison places would lead to 18-year-olds being thrown into adult jails without the support needed to cut reoffending rates.
Angela Sarkis, national secretary of the YMCA in England, said: "Overcrowding particularly hits young adult offenders who may be moved on their 18th birthday from a juvenile offenders' institution to an adult prison.
She called for greater use of community sentences for less serious offenders to keep them out of prison.
Official figures suggest that there are about 9,000 offenders aged between 18 and 21 in prison. The Prison Reform Trust warned that young people faced being pushed into the "rushing water" of the adult prison system.
William Higham, head of policy at the trust, warned that centres for 18 to 21-year-olds faced closure. He said "It is the age at which they can either get off or become confirmed in crime."Reuse content