• Since 2021, HMPPS has rapidly expanded electronic monitoring, now tagging around 29,000 people – but thousands of individuals may not be actively monitored despite having a tagging requirement.1 
  • Demand is set to rise significantly from September 2026 to help ease the prison capacity crisis – making it vital that the current issues with the system are addressed. 
  • The NAO recommends that the MoJ and HMPPS take a system-wide approach, strengthen performance monitoring, tackle inefficiencies and put robust contingency plans in place to manage system risks. 

Uncertainty over how many people are not being monitored, combined with wider inefficiencies in the Ministry of Justice’s electronic monitoring service, is wasting resources and increasing public protection risks. The National Audit Office says this raises concerns about plans to expand a system that has grown quickly but is not yet working effectively.

Electronic monitoring, or ‘tagging’, uses technology to remotely monitor a person’s location and compliance with court requirements. In September 2025, the MoJ announced plans to significantly expand electronic monitoring as part of the Sentencing Act 2026, which aims to ease prison pressures by managing more offenders in the community.

But poor early performance from one of its external contractors, Serco, meant that between August 2024 and July 2025, individuals were not tagged on time and officials were not notified of potential breaches in a timely manner.2 During this period, the backlog of visits to fit, check or remove tags increased significantly to a peak of 7,000 visits in October 2024 – before returning to fewer than 400 in November 2024.

HM Prison and Probation Service (HMPPS) has worked with Serco to improve performance and reduce backlogs in fitting tags. But supplier performance improvements alone are not sufficient to ensure the wider system is working as intended.

The number of unmonitored individuals is also a concern: as of March 2026, HMPPS was reviewing around 8,900 cases – 24% of those required to be tagged – to determine the number of unmonitored cases.3

Police and probation officers often lack information or capacity to respond quickly to breaches. Inefficiencies in the system and a lack of prioritisation add to this challenge, with high volumes of alerts and breach notifications generating significant work with limited value. For example, where outcomes are recorded, nearly half result in ‘no further action’. On visits, the NAO observed that both serious and minor breaches were often treated in the same way.

There is also no shared understanding of what a more responsive electronic monitoring system should look like or how it should be measured. For example, Serco’s contract does not require it to provide officials with details of an individual’s breach until 29 to 53 hours after it occurs.

The wider system is inefficient, with many errors in tagging orders and a low success rate for tagging people, causing delays in getting individuals tagged. In February 2026, although Serco met its 95% timeliness target for tag-fitting visits, it was only successful in fitting tags on 62% of the individuals it visited within its two attempts.

In September 2025, the MoJ estimated that up to 22,000 additional people will need to be tagged per year from 2027. To deliver this increase, HMPPS is aiming to stabilise the service, build the foundations to scale up activity and transform the programme, including through adopting new technology and data.

The government has allocated up to £175 million to fund the expansion over the 2026-2029 spending review period, which includes developing a series of pilots. For example, it plans to strengthen management of domestic abuse offenders through tags that can monitor their proximity to their victim.

However, key elements of the system are not yet working effectively – for example, significant understaffing persists, including an estimated shortfall of around 2,200 probation staff as of March 2026. There have been concerns about whether the system can scale up safely.

The report from the independent public spending watchdog 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.

“Electronic monitoring is central to managing pressures on prisons, but it is not working effectively, creating risks to public protection. 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.”

Gareth Davies, head of the NAO

Read the full report

Electronic monitoring: improving resilience to meet increasing demand

Notes for editors

  1. The Electronic Monitoring population in England and Wales increased significantly from around 13,400 in January 2021 to 28,700 by March 2026
  2. In October 2023, MoJ awarded new contracts to Serco, to fit tags and monitor tagged individuals; and Allied Universal Electronic Monitoring to supply the tags and monitoring system.
  3. HMPPS told the NAO that these cases under review include some cases which remained active by error. HMPPS has a new definition of ‘unmonitored’. This now includes active Electronic Monitoring cases where an individual has not been tagged, and those whose device has been disconnected for 14 days or more, for example because they have not charged their tag. Individuals with disconnected devices are currently included within the tagged caseload and are not included within these 8,900 cases under review. HMPPS expects to publish statistics on the number of unmonitored individuals in late July 2026.