Professor Dame Angela McLean, Chief Scientific Adviser to the Ministry of Defence and a participant of SAGE, told the Science and Technology Committee in February 2021 that the tier system waited until prevalence was high before any action was taken, implying this was a flaw with the tier system: What we did with the tier system was we waited until prevalence—the number of people in a place—was high before putting it into a more restrictive tier. We should have said, “Ah, look, in this part of the country the number of infections is starting to grow”—we have a rather exquisite tool for measuring that—and put it into a higher tier while its prevalence was still low.187 Dame Angela’s point was also noted in SAGE minutes. On 19 November 2020, SAGE said that “evidence shows that the earlier and more rapidly interventions are put in place, and the more stringent they are, the faster the observed reduction in incidence and prevalence.”188