The Ministry of Justice has admitted for the first time that thousands of offenders ordered to wear electronic tags were not actually fitted with the devices. According to the new data, 5,450 offenders — just under one in seven of the 37,600 who should have been tagged — were not wearing monitoring devices at the end of March. The disclosure is significant because it undermines the credibility of Labour's sentencing reforms, which rely heavily on electronic tagging to justify sending fewer criminals to prison.

While some cases have legitimate explanations, such as an offender having been returned to jail, others stem from less reassuring reasons, including the offender not being at home when contractors arrived to fit the device. The MoJ has not broken down how many fall into each category. The revelation is awkward for ministers, given that prisons minister Lord Timpson claimed in March that the reforms represented the "biggest expansion of tagging in British history" and would ensure the most dangerous offenders were watched more closely than ever.