• The prison and health services are facing substantial, increasing and rapidly changing threats from illicit drugs in prisons, including the rising prevalence of synthetic drugs and the use of drones – in April 2025 approximately 40,000 people in prisons in England and Wales (50%) had an identified drug problem.
  • HM Prison and Probation Service (HMPPS) has significantly underspent on two investment programmes that aim to reduce drug harms in prisons
  • In 2024-25, 24% of prisoners with potential substance misuse needs waited over three weeks for NHS England (NHSE) to conduct a triage health assessment, following reception screening
  • The National Audit Office (NAO) recommends that security weaknesses should be addressed with more urgency and there should be a renewed commitment to cross-government partnership working, to direct resources to where they will have greatest impact.

Progress on reducing drug harms in prison will depend on stronger coordination between HMPPS and health services, reacting urgently to security weaknesses and using information on drug prevalence and health needs more consistently to prioritise spending, says the NAO.

In its latest report – The costs of tackling drug harms in prisons – the independent public spending watchdog examines how effectively the prison and health services are using public funds to tackle drug use within prisons, how funds are prioritised and how well the two services work together.

In 2025-26, the government committed around £40 million of investment to high-risk prisons for better security measures. These include window grilles and netting, to counteract criminal use of drones, sightings of which have increased by over 750% between 2019 and 2023, and by 43% between 2023-24 and 2024-25.

HMPPS has been too slow in responding to urgent threats and prison governors told the NAO that they do not have sufficient resources. The NAO heard examples of broken security equipment (e.g. x-ray scanners for prisoners’ luggage) not being repaired for many months and of work to improve window security taking several years.

Despite the challenge that illicit drugs in prisons poses, HMPPS has significantly underspent on two investment programmes. Between 2019-20 and 2021-22, HMPPS spent only 75% of its £100 million security investment programme budget, with the largest underspends in gate security.

HMPPS was also allocated £114 million between 2022-23 and 2024-25 for prison-based and cross-cutting initiatives as part of the cross-government drug strategy From harm to hope. The actual budget was revised to £97 million to make savings and, of this, HMPPS spent only £67 million (69%).

NHSE spending on mental health and substance misuse services in prisons was £226.4 million in 2024-25. Looking at the last five years, this represents a cash increase compared with the £202.9 million spent in 2020-21, but a real terms decrease of 5%.

In 2024-25, NHSE recorded nearly 160,000 substance misuse appointments as ‘did not attends’, accounting for around 35% of all appointments. This can be for a variety of reasons, including the prisoner choosing not to attend, but has the potential for negative impacts on people’s health and wellbeing, the efficient use of health and prison staff resources, and the prison regime.

NHSE does not use regional health needs assessments to decide its funding allocations, despite there being a significant regional variation on spending on substance misuse services. The NAO found that in 2024-25, the London region spent 72% more on substance misuse treatment per prisoner than the East of England. NHSE has not investigated this variation.

HMPPS spends an estimated £8 million a year on monthly random mandatory drug testing on prisoners (see ‘Notes to editors’). However, prison staff told the NAO that these random tests were operationally resource intensive. HMPPS has been trialling more innovative methods of identifying drug prevalence, by testing prison wastewater for traces of illicit drugs.

The physical design, age and poor condition of some prisons make them vulnerable to drug ingress, particularly older prisons and listed buildings. The maintenance backlog across the prison estate has also doubled from £0.9 billion to £1.8 billion between 2020-2024.

The NAO’s report recommends:

  • The prisons and health services should make a renewed commitment to cross-government partnership working to support better alignment of incentives and shared goals
  • HMPPS should respond with more urgency to identified security weaknesses at specific prisons, including broken windows or inadequate window grilles
  • HMPPS should improve information on prevalence to prioritise funding where it is move effective
  • NHSE should strengthen commissioning of drug treatment services by refocusing Health Needs Assessments, refining costing formulae to reflect differing prison needs, and introducing costed key performance indicators (KPIs) to ensure providers deliver value for money
  • HMPPS and NHSE should draw on robust evaluation to understand what works and encourage best practice

"The proliferation of illicit drugs in prisons undermines rehabilitation, damages health, and destabilises prison environments. Yet too many of the basic controls and interventions are not being done well enough - from repairing critical security equipment to aligning health and operational priorities.

"Our recommendations are designed to help the prison and health services direct resources to where they can have the greatest impact on this serious problem."

Gareth Davies, head of the NAO

Read the full report

The costs of tackling drug harms in prisons

Notes for editors

  1. In April 2025 approximately 40,000 people in prisons in England and Wales (50%) had an identified drug problem.
  2. Between December 2022 and December 2024, the Prisons and Probation Ombudsman investigated 833 deaths, of which 136 (16%) were drug-related.
  3. In 2024-25, HMPPS reported 26,348 individual drug finds, 25% more than the previous 12 months.
  4. ‘Since 1999, HMPPS has carried out random mandatory drug testing on prisoners every month, the full cost of which it estimated in 2023 was around £8 million a year’. 

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