This article investigates the impact of national lockdowns on Covid-19 transmission in the UK. The authors use a susceptible-infected-removed (SIR) model to estimate the instantaneous reproduction number (Rt) from February 2020 to July 2021. Their findings suggest that lockdowns effectively reduced transmission rates after 2-3 weeks, with Rt falling significantly during each of the three national lockdowns. The study also indicates that longer lockdowns had more lasting effects on keeping Rt below 1. While acknowledging limitations in data quality and model assumptions, the authors conclude that policymakers should continue to consider Rt in decision-making processes, balancing virus control with economic and mental health concerns.