Thanks very much Oliver for your response. I totally agree that factors leading to underestimation of the number of introduced lineages should be much stronger than those leading to overestimation in UK and others highly connected locations. Maybe an indirect measure of the relative importance of the “multiple importations” vs “local divergence” hypotheses could be obtained from the proportion of UK transmission lineages that arose before and after implementation of international air travel restrictions between UK and other European countries. Congratulations again for this amazing work.