The Ministry of Justice’s plans to rapidly expand electronic monitoring of offenders to ease pressure on prisons could waste money and put the public at risk because the system is not working effectively, according to the National Audit Office.
The public-spending watchdog said the MoJ and HM Prison and Probation Service currently tag around 29,000 people as an alternative to a custodial sentence. But it said thousands of those individuals may not be “actively monitored”.
More than twice as many offenders are currently subject to electronic monitoring than was the case in 2021. However, under plans announced in September last year the MoJ estimated that up to 22,000 additional people will need to be tagged per year from 2027.
To deliver the increase, HMPPS is aiming to stabilise the service and build the foundations to scale up activity and transform the programme, including through adopting new technology and data.
The expansion has funding of up to £175m allocated in the years to 2029. However, the NAO said “key elements” of the system are not yet working effectively. It said “significant understaffing” persists, including an estimated shortfall of around 2,200 probation staff as of March this year, with concerns about whether the system can scale-up safely.
The NAO said that between August 2024 and July 2025, “poor early performance” by tagging contractor Serco meant that some individuals were not tagged on time and officials were not notified of potential breaches in a timely manner.
It said that in October 2024 there was a backlog of 7,000 visits to fit, check or remove tags, although the figure reduced to fewer than 400 the following month. The report notes that while HMPPS worked with Serco to improve performance and reduce backlogs, supplier performance improvements alone are not enough to ensure the wider system is working as intended.
The NAO added that the number of “unmonitored individuals” is also a concern. It said that, as of March this year, HMPPS was reviewing around 8,900 cases – almost one quarter of the total number of people supposed to be tagged – to determine the number of unmonitored cases.
The MoJ said today that its statistics suggest the total number of unmonitored individuals is approximately 5,450.
The report concludes that further expansion of the electronic monitoring system will not be efficient or effective unless the MoJ and HMPPS work with partners to address weaknesses in governance, data quality and system-wide inefficiencies to support a more reliable and responsive service.
NAO head Gareth Davies said “significant inefficiencies” are present across the system, wasting staff time and taxpayers’ money, and limiting performance improvements.
“Electronic monitoring is central to managing pressures on prisons, but it is not working effectively, creating risks to public protection,” he said. “Improvements are required to ensure that those who should be monitored are monitored and that breaches are responded to effectively.
“The MoJ and HMPPS should address the inefficiencies and risks identified in our report before expanding electronic monitoring.”
An MoJ spokesperson said the government “inherited a failing tagging system with record backlogs” in 2024 and the NAO report shows the hard work that has gone into fixing the situation.
“Public protection is our priority, which is why we’re investing £100m in electronic monitoring, tagging offenders before release for the first time and strengthening victim protections via new alert systems – all of which will help cut the number of unmonitored offenders,” the spokesperson said.
“This is in addition to our record £700m investment in probation, recruiting 2,300 trainee probation officers over the last two years, and recruiting a further 1,300 this year – making sure the Probation Service has the resource it needs to keep dangerous offenders under closer surveillance than ever before.”