By Danny Shaw
BBC home affairs correspondent
Lord Woolf said the system was being used "routinely"
Public confidence in the criminal justice system is being eroded by the early release scheme, the former Lord Chief Justice has told the BBC.
Almost 50,000 offenders have been let out under the scheme - known as End of Custody Licence (ECL).
It was introduced 18 months ago to reduce inmate numbers at the height of the prison overcrowding crisis.
But Lord Woolf said people had become "conditioned" to the early release scheme.
"I think we've now become conditioned to executive release," Lord Woolf said.
"It's now being used routinely and we've got embedded in our system a situation of the judges sending prisoners into prison by the front door and the executive releasing them by the back door, and that doesn't make sense."
Under ECL, less serious offenders can be freed two-and-a-half weeks before they have reached the halfway point of their prison term - the stage at which most prisoners are released.
But John Thornhill, chairman of the Magistrates Association, said ECL blunted the impact of prison sentences and was a source of frustration for magistrates.
"To release (offenders) earlier on the decision of a member of the executive rather than by a member of the judiciary... does undermine confidence in those sentences," he said.
Mr Thornhill called for ECL to be "phased out immediately" because there was now sufficient capacity in the prison system.
Figures published last week showed there were more than 2,000 spare jail places.
When the scheme was introduced in July 2007, prison cells were in such short supply that police stations and courts were used to accommodate prisoners overnight.