erd and lrd
The parole board can only recommend release between a prisoner's ERD (earliest release date) and their LRD (latest release date).
Simplifying a lot: for a sentence over 4 years, the ERD is the halfway point. The LRD is the four year mark.
The prisoner may well have enough evidence at the 2-year mark that they can be released under license for the next two years. If the parole board agree, society saves a fortune (around £65,000 in total) in not keeping that prisoner banged up for the second two years.
If the parole board does not get around to hearing the case until the three-year mark, that's just cost all us tax payers over £30,000.
Of course, if the prisoner does not have the evidence, they stay in until their LRD -- which is a date set by the courts.
Upposts in this thread have suggested that the prison service should be able to overrule the Courts on the LRD. If they could do that, they could jail YOU with immediate effect and no habeus corpus to save you.
That's a dangerous power to bestow on a prison service.