Allowing electronically-tagged prisoners out of jail early may be undermining trust in the criminal justice system, a report has argued.
Lord Coulsfield, who headed a review, said the scheme interfered with the court's decision.
He said it could suggest to the public "that what the court says is not what actually happens".
And Custody Plus, which combines a short jail term with supervision in the community, should be reviewed, it said.
Lord Coulsfield said Custody Plus sentences had "little or no value" in deterring or reforming criminals.