Equipment used to monitor dozens of offenders or suspects in the community is faulty, it has emerged.
Straps used to secure electronic monitoring tags could incorrectly trigger an alert suggesting they have been tampered with, the Ministry of Justice said.
Testing indicates that more than 100 of the straps are faulty, while it is possible that a small number of individuals may have been wrongly placed behind bars.
The Liberal Democrats claimed it was a "colossal blunder", while the Government insisted there was no risk to the public.
Justice Minister Sam Gyimah said there was a "small chance" that some "enforcement action" might have been taken against an offender or suspect in response to a false report of a tamper.
"It does not mean an individual will have been automatically sent to custody," he said.
"A single tamper alert without any additional evidence of an escalation of risk is likely to result in an alternative outcome, such as a warning letter. So it is unlikely that a first tamper on its own will result in an offender being recalled."
Officials said that if any individuals had been returned or sent to custody, the number was likely to be small.