A technological problem, revealed in a letter from the Home Office minister Paul Boateng, means that signals from the tags are blocked by the metal objects, or by high altitude, setting off false alarms in the security base station.
As a result, about 20 prisoners have been wrongly sent back to prison after being placed on the Home Detention Curfew (HDC) scheme, a government initiative designed to reduce prison overcrowding and cut reoffending.
In his letter to the National Association of Probation Officers (Napo), Mr Boateng said: "The difficulties to which you refer may occur when the tag loses contact with the site monitoring unit due to obstruction caused by certain metals, for example, metal baths and kitchen ranges. This can result in the offender being registered as out of range."
He says that tagged offenders who live in large buildings are being asked to restrict their movements to certain rooms so that the tag signal is not lost. Otherwise, he says, the Prison Service may consider recalling them to prison.
Only about 30 per cent of prisoners eligible for HDC have been released under the scheme, far below the 70 per cent figure which had been expected when the project began in January.
Harry Fletcher, a spokes-man for Napo, said: "The Home Office want to see a massive expansion of tagging but they will need to improve their technology and assessment procedures if it's going to be credible. Even if they do, it won't affect crime rates because it's only a punishment in its own right and does nothing to change criminal behaviour."
A Home Office spokeswoman said that HDC had been a "success" and that only a "very small percentage" of offenders had been wrongly recalled because of monitoring failures.Reuse content