All prisoners convicted of offences committed after April 4 last year are released on licence at the half way point of their sentence.
Probationers who break licence condition will be returned to jail
Before their release the Probation Service will meet with other agencies to assess the offender's risk and decide on their licence conditions.
Some, including the most high risk offenders, will be told they must reside at a bail hostel where they will be monitored by trained staff.
The Government says this is a better alternative than placing offenders, which include paedophiles, straight into a community unsupervised.
But critics argue that placing a number of paedophiles in the same hostel can increase the chances of re-offending and put children living nearby at increased risk.
Offenders are required to sign a document agreeing to the rules of the hostel they are told to reside at, which differ between individual premises.
Generally each of the 104 hostels in England and Wales has a curfew running from 10pm until 6am when residents must be inside.
Residents must also agree to acceptable standards of behaviour. Repeated breach of the rules will result in an offender being returned to jail.
All hostels have CCTV cameras in communal areas, alarmed doors and staff trained to recognise signs that a resident may re-offend or be re-offending.
Hostel staff have no power to monitor the movements and behaviour of an offender when they are out of the hostel outside of their curfew times.
If a curfew is breached or an offender is believed to be posing a risk the police are informed and the person may be taken back into custody.
Offenders may have specific conditions applied to them by the Probation Service.
They can extend the hostel's curfew hours so that an offender has to be indoors at other periods. For example school arrival and leaving times.
Exclusion zones can also be used to prevent a person from going near a particular place, which may be a house, school or playground.
An offender can also be banned from having contact with a particular named individual or generally children below a certain age.
The Probation Service can also ask for an offender to be fitted with an electronic tag as a way of enforcing a curfew.
A transmitter is placed at the offender's hostel and if the tag is not within range at a certain time the alarm is raised.
Offenders are also appointed individual Probation Service supervisors who meet and interview them at designated times each day, week or month.
The officer will continually assess the offender to make sure he or she does not pose a risk.
Dick Whitfield, chairman of the Howard League for Penal Reform, said the Probation Service had a "very tough" job.
"If people are deemed fit to be released from prison you can't monitor them every minute of the day," he said.
"Otherwise they shouldn't be out. What needs to happen is the Probation Service having enough resources to do the job.
"Often there are just three members of staff, usually not probation officers, looking after a hostel with 30 people. That needs to change.
"If you have 30 paedophiles in the same place with so few staff it's impossible to monitor everything that's going on and can be dangerous."