Background Hepatitis C virus (HCV) transmission in the UK is driven by injecting drug use. We explore HCV testing uptake amongst people who inject drugs (PWID) in England, Wales and Northern Ireland, and identify factors associated with i) ever having an HCV test amongst people who have ever injected drugs, and ii) recently having an HCV test (within the current or previous year) amongst people who currently inject drugs (reported injecting drugs within the last year). Methods We analysed data from the 2019 ‘Unlinked Anonymous Monitoring Survey’ of PWID, using logistic regression. Results Of 3,127 PWID, 2,065 reported injecting drugs within the last year. Most (86.7%) PWID had a lifetime history of HCV testing. In multivariable analysis, higher odds of ever testing were associated with: female sex (aOR=1.54; 95%CI 1.11-2.14), injecting duration ≥3 years (aOR=2.94; 95%CI 2.13-4.05), ever receiving used needles/syringes (aOR=1.74; 95%CI 1.29-2.36), ever being on opioid agonist treatment (aOR=2.91; 95%CI 2.01-4.21), ever being imprisoned (aOR=1.86; 95%CI 1.40-2.48) and ever being homeless (aOR=1.54; 95%CI 1.14-2.07). Amongst PWID who had injected drugs within the last year, 49.9% had recently undertaken an HCV test. After adjustment, factors associated with higher odds of undertaking a recent HCV test included: injecting crack in the last year (aOR=1.29; 95%CI 1.03-1.61), experiencing a non-fatal overdose in the last year (aOR=1.39; 95%CI 1.05-1.85), ever being on opioid agonist treatment (aOR=1.48; 95%CI 0.97-2.25), receiving HCV information in the last year (aOR=1.99; 95%CI 1.49-2.65) and using a healthcare service in the last year (aOR=1.80; 95%CI 1.21-2.67). Conclusion Results suggest that PWID who have experienced homelessness and incarceration – amongst the most vulnerable and marginalised in the PWID population – are engaging with HCV testing, but overall there remain missed testing opportunities. Recent initiates to injecting have highest HCV infection risk but lower odds of testing, and peer-education may help target this group.