That comes from the UK government covid data site which says there's been a 10% drop in the last 7 days. https://coronavirus.data.gov.uk/details/testing
So there has been a drop, but, arguably, it's to be expected for, at least, two reasons: 1) schools are out; 2) if cases are indeed going down people are less likely to get tested.
Edit - to add, the share of positives per test is dropping despite the a drop in testing numbers on the whole. So I wouldn't want to make the claim that the drop is simply a result of fewer tests.