May I now turn to the app? This really matters because unless someone with covid-19 can name and identify everybody they have been in contact with, the app is the only way of tracing unknown contacts. My hon. Friend Peter Kyle made precisely that point yesterday. He gave the example, “How on earth do you trace everyone in close contact at a seafront or in a park without an app?” Up until last week, the Government maintained that the app was “critical—another of their slides—but at the weekend the Health Secretary downplayed the app, saying it was only ever additional support. So which is it: critical or not?