The new cases are coming from people with milder disease self-isolating at home with their families who then continue the infection. The problem lies with the fact that we got the worse of both worlds, we got a half hearted ‘lockdown, where we should have had an initial total curfew, as they did in France for example, and also we should have had proper quarantine for the mildly affected (in hotels or in the underused nightingale hospitals) rather than self isolation at home which is more likely to continue the spread. Notice that Hancock says, test, track and trace, sort of meaningless really. So you test and you track and you trace. You should be test, quarantine and trace, the meaning of track in this context is vague.
This government is incompetent, They have never handled this properly from day one. There is no proper scrutiny as they stole a majority in parliament and I bet you they will get away without an enquiry and say that is unnecessary, after all it will take Tories to dissent and rebel against the government in parliament to vote for an enquiry. And the danger is that the whitewash has already started. Boris now having survived his own folly, with a young child, is already painting himself as the beacon of how to deal with covid-19, from personal experience.
But I am rambling, sorry.