Up to 1,200 criminals will be released early today to relieve the overcrowded prison system.
The former lord chancellor Lord Falconer conceded earlier this month that the government would have to cut short some offenders' sentences after the prison population reached a record 81,000.
His successor Jack Straw confirmed today the scheme would continue for "some time", while the government continues to expand the number of prison places available.
Mr Straw said eligible prisoners would be "carefully selected" by prison governors and only released 18 days shy of their full sentence.
Prisoners sentenced to between four weeks and four years will be eligible for early release, affecting up to 25,000 offenders a year.
Speaking to BBC Radio 4's Today programme, Mr Straw said around 1,000 prisoners a month would be released early, starting today, and this would continue for "some time".
"This will carry on until we do get stability in the prison population," he said.
The Conservatives have rounded on the scheme and laid the blame firmly on a lack of Home Office funding.
Shadow home secretary David Davis said: "The first act of a Brown government is for over 1,000 offenders to be released early.
"This is a consequence of the new prime minister's refusal to adequately fund our prisons when he was chancellor, and it is the public who are now paying the price with their safety."
The Liberal Democrats pointed to the government's reliance on prison as its punishment of choice.
The Liberal Democrat's justice spokesman, Simon Hughes, said: "This is a fiasco that has been a decade in the making. A series of Labour home secretaries have failed to take the action that would have prevented the need for these emergency measures.
"The government's obsession with wanting to look tough on crime has had the remarkable effect of leaving our prisons full to bursting and fear of crime at an all-time high."
Former prime minister Tony Blair admitted the prison service had been under pressure due to the 25 per cent increase in sentencing, increased use of indeterminate sentences and penal sanctions for offenders breaking parole.
Labour built 20,000 more prison places over the past decade, after inheriting a prison population of 61,500.
To ease overcrowding, Gordon Brown announced a further £240 million in one of his final acts at the Treasury. It will be used to build 1,500 prison places, with a further 8,000 planned by 2012.