More than 16,000 prisoners have been released early since the government launched the scheme designed to increase capacity in jails.
Figures published today show 16,197 offenders in England and Wales were freed early in England and Wales between the scheme's launch in June 2007 and December.
Under the custody licence scheme prisoners are freed 18 days early to ease pressure on the prison system.
Ministers have maintained offenders convicted of violent or sexual crimes will not be eligible for early release but today's figures show 3,000 prisoners were released early while serving time for violent crimes.
Of the 16,000 freed early, 215 went on to re-offend, committing 301 crimes. A further 117 were ordered to return to jail.
Shadow justice secretary Nick Herbert said the early release scheme had put public safety at risk and failed to deal with prison overcrowding.
He argued: "This early release scheme must be scrapped immediately and sufficient prison places provided so that public safety comes first."
The Conservatives blame the government for prison overcrowding, arguing it has failed to build adequate prison capacity.
Justice secretary Jack Straw today confirmed the government plans to build three new 'Titan' prisons by 2014. A consultation on their design will be launched this April.
Mr Straw insisted the government is on course to deliver a net increase of 15,000 new prison places by 2014.
The Liberal Democrats also condemned today's figures, arguing time "served should be dictated by the severity of the crime, not by how much room there is available in our prisons".
But Lib Dem justice spokesman David Heath blamed the government's policies for increasing the prison population, calling on ministers instead to increase secure mental health provision and drug treatment places.
Mr Heath said: "Ministers are relying on short-term solutions and desperately trying to convince themselves they can simply build their way out of this crisis."
Mr Straw today committed the government to a new strategy designed to get prisoners off drugs, as well as helping offenders into work.
He promised a drive against drugs, including treatment in prison but also greater efforts to control supply.
Ministers will also work with employers from all sectors, encouraging them to take on offenders.
Mr Straw said: "The announcements I am making today signal a major drive to overcome some of the barriers to the rehabilitation of offenders.
"Our primary aim in doing so is further to aid the work we are already doing on cutting reoffending. These measures are focused on tackling drug use among offenders and providing opportunities for offenders to learn the new skills which might help them to a life away from crime outside prison."
The British Medical Association (BMA) welcomed the government's commitment to drug rehabilitation programmes, pointing out six in ten prisoners enter prison with a drug depending problem.
But Dr Clare Jenkins, chair of the BMA's civil and public services committee, cautioned: "There is a lack of detail in the secretary of state's statement that will cause concern among prison doctors.
"Rehabilitation services across the country need more funding, more staff and a greater use of technology, such as an electronic medical records system. There is also a desperate need for better organised support networks and monitoring services in the community."