[Question] What made the UK COVID-19 case count drop?

According to Google COVID-19 data, something made COVID-19 cases drop after July 21, 2021. To me that event is unexpected given that the measures where in the process of being lifted and I wouldn’t expect that to coincide with citizens engaging in more risk avoiding behavior.

If there’s a factor bringing cases down we don’t know, understanding what the factor is could be very valuable. Does anybody have a good explanation for why the cases dropped?