HMRC has not made a robust assessment of the additional costs of implementing the reforms. HMRC states that the IR35 reforms increased tax revenues by increasing the number of people employed for tax purposes, but it is unclear to what extent employment patterns have been affected by other factors. EU Exit, the COVID-19 pandemic and other changes in government to reduce use of contractors mean HMRC cannot be certain to what extent the increase is due to the reforms. There is also not a complete picture of the costs of the reforms against which the benefits could be compared. The government introduced the reforms because it considered it too costly for HMRC to oversee an effective compliance regime with each individual PSC. HMRC also concluded that hiring organisations could administer the rules for less cost than PSCs doing it themselves. However, HMRC’s modelling of the cost to hiring organisations works out at just £35 a year per PSC, based on a theoretical minimum needed to comply. HMRC does not know what it actually costs all parts of the labour supply chain to administer the reforms in practice. Recommendation: In light of actual experience, HMRC should produce and present to Parliament a cost-benefit analysis of the reforms that reflects the actual costs of compliance to HMRC itself, hiring organisations, workers, and others in the supply chain.