There's one other angle too here - a future version of the UK app will give people feedback on their level of distancing via a "social mixing score", which is b

There's one other angle too here - a future version of the UK app will give people feedback on their level of distancing via a "social mixing score", which is basically the number of unique people they were recorded as being in contact with per day. This looks like it will give people an idea of "You were close to X people today, and really close to Y people". "Close" will be locally determined, probably based on the RSSI model and duration of contact. This will give people feedback on how well they are distancing. There's a lot of research which shows people struggle to know if they are doing well without feedback, and that people's perception of how well they can do it will influence if they try. Couple this with a differential privacy daily voluntary "upload" (add a random, zero-mean number sampled from a normal distribution to their daily number) and people can find out if they're doing well, or if others are reducing contact more. NHS also gets an idea of average number of contacts and close contacts, and nobody actually needs to reveal their own number.