Entitlement to benefit is complex and a minefield for the claimant.  However, before release, for long term prisoners, some help is given to start the application. 

The first thing you should do on release is make a claim for benefit.  If you have sufficient stamps on your card you should go to the Job Centre and commence a claim for Job Seekers Allowance.  If necessary you should go to the Social Security (DSS) and claim benefits - The Social!  You may also need to claim Council Tax Allowance and Rent Allowance.  You can claim these even if you are not living in a Council House.

Do these on day one of your release if you can.

Unless you are a university graduate with an extremely high IQ you will need help and advice about state aid.  Most County Councils give help in this direction and do ask at your local library for the contact point.  Their officers can often visit you at home.  The Citizen's Advice Bureau is also a good place to get advice free of charge.