The prison population has hit a new high, with the number of inmates reaching 75,550 - exceeding the record set a year ago by six.
More are being jailed for violence, criminal damage and arson
After peaking in April 2004, numbers of inmates in England and Wales had begun to fall, but they increased over the past few months, BBC News has learned.
The number of male prisoners has risen sharply and more inmates are serving long sentences, including life terms.
But the Prison Service said there were enough spare cells to manage the rise.
The increase in the prison population may also be due to more offenders being jailed for violence, criminal damage and arson.
Of the total prison population, 4,489 are women, down by 183 from the record set last year.
The current prison capacity is around 77,000 and is due to rise to just over 80,000 in three years, a Prison Service spokeswoman said.
There had been an increase of 16,000 in the number of prison places since 1997.
The spokeswoman said some of its places were currently out of use for refurbishment, while some privately-run jails had cut their capacities to reduce crowding.
"This does not currently pose problems as the prison population remains below its operational capacity," she said.
However penal reform campaigners say the majority of prisons remain overcrowded, hampering efforts to rehabilitate prisoners and prepare them for release.
Juliet Lyon, director of the Prison Reform Trust, said there were more than 17,000 male inmates who were being paired in cells designed for only one person.
She added that the number of women being jailed had more than doubled in the last 10 years.
"The government must look for solutions outside the criminal justice system if it's serious about reducing prison numbers," she said.
"It has to divert petty offenders into mental health or drug treatment programmes that they so badly need."
She said 58% of prisoners reoffend within two years of their release. Among young offenders, that figure rose to two-thirds.