Ministers have covered up poor results from a pilot project carried out in the West Midlands designed to keep tabs on paedophiles and other sex offenders.
The £2.5 million project using a new breed of electronic tags which work by satellite suffered a host of technical problems. The signal was blocked by clouds, trees and buildings.
Leaked documents obtained by the Daily Mirror showed Ministers ordered that the public should not be told the results.
A memo to Home Secretary Charles Clarke recommended extending the scheme to improve the outcomes, adding: "We have not sought to publicise the pilot scheme
... due to the risks of negative media coverage of the poor results."
The Home Office press office had "strongly advised against any publicity", it said.
The memo reminded Mr Clarke: "You were not prepared to take those risks.
"We recommend that you delay any media announcement until interim results significantly improve."
Former Home Secretary David Blunkett described the pilot as a "prison without bars" when he launched it in the West Midlands, Manchester and Hampshire last September.
Up to 120 offenders at any one time were due to be fitted with satellite tags to pin-point their exact location, 24 hours a day.
The technology was used for sex offenders in the Manchester pilot only, and for domestic violence offenders and prolific offenders in the other two zones.
The leaked report to Mr Clarke said: "If the subject is between tall buildings, a canyon effect can prevent accurate location.
"Leaf cover and cloud cover can mask the strength of the signal.
"Location cannot be obtained on planes, some intercity trains and the Underground.
"Location is usually lost inside buildings."
The system features electronic ankle tags with a wireless connection to a mobile phone carried by the offender at all times.
The network feeds back a set of co-ordinates to the tracking station so officials can see the criminal's exact location.
An alarm is triggered if the phone, which is linked to the supervisors' call centre, is separated from the tag.
And in theory the system would sound an alarm if, for example, a tagged paedophile approached areas from which he or she had been banned, such as a playground or school.
It was also intended to provide evidence that a tagged burglar was near the scene of another offence which he or she was suspected of committing.
The leaked report, dated July 18, this year, revealed of 178 offenders who had been satellite tagged so far, 83 had been recalled to prison, 66 were still being tracked and only 29 had successfully completed the course.
A Home Office spokesman said: " Satellite tracking was never designed to be a replacement for any other form of supervision and management.
"There have been initial difficulties with the technology, which we had always envisaged.
"But the technology is advancing all the time and recent developments have been introduced which has increased the likelihood of obtaining a signal in adverse weather."