There's already "Weekly number of people receiving a PCR test and positivity" at the Testing in England page.shpalman wrote: ↑Sat Aug 14, 2021 6:53 amEngland’s R number between 0.8 and 1.0 based on last week when cases were coming down, which means that cases were coming down, except of course that they're obviously slowly going up again now as you can see by just looking at the data without needing to do any fancy analysis apart from assuming the testing rate is roughly constant.
It's now more than 8% whereas in early May it was about 0.8%.* You can see that the number of people tested does vaguely follow the number of new positives, but then the positive rate also follows the number of new positives. So when there are more cases, more tests get done and a greater proportion of them come back positive. So it's not that you seem to have more cases because you're doing more tests, but rather the increasing number of suspected cases means more testing is required but testing capacity can't vary exponentially across orders of magnitude in the way that case numbers can.
* - this metric peaked at around 40% during the first wave and 18% in the second wave.