AbstractThe effective reproduction number$ R $was widely accepted as a key indicator during the early stages of the COVID-19 pandemic. In the UK, the$ R $value published on the UK Government Dashboard has been generated as a combined value from an ensemble of epidemiological models via a collaborative initiative between academia and government. In this paper, we outline this collaborative modelling approach and illustrate how, by using an established combination method, a combined$ R $estimate can be generated from an ensemble of epidemiological models. We analyse the$ R $values calculated for the period between April 2021 and December 2021, to show that this$ R $is robust to different model weighting methods and ensemble sizes and that using heterogeneous data sources for validation increases its robustness and reduces the biases and limitations associated with a single source of data. We discuss how$ R $can be generated from different data sources and show that it is a good summary indicator of the current dynamics in an epidemic.