thread What I don't understand about this
Is that 750,000 people volounteered to help the NHS. And while I can see that some info is sensitive, but a bit of training and an NDA would surely cover that... I mean mostly they will be phoning branches of Tesco and offices..

And 5 a day? Sounds like nonsense, I'm pretty sure I could give you the list of everywhere I've been in the last 2 weeks in about 15 minutes and a single person could call them in a day, call it 2 for arranging appointments and that would mean we have 10 people working on this?

I mean who is it that gets Ill and doesn't tell all Thier friends, relatives and workmates anyway?

The tricky bit of tracking would be collating the info to find hotspots like a corner shop that is spreading it or something... But that sounds like a job for an open street map overlay or a big bit of paper and some pins.
permalink the bit where it falls apart
is exactly places like Tesco. How on earth do you manually trace everyone that was in the supermarket at the same time as an infected person (without either the good app that they don't seem to want, or pre-exsting mass surveillance like South Korea and Taiwan)?
And it is clear that the contractors hired to oversee it all have been shit.

permalink the last part is certainly true
the tesco problem is tricky, even with the perfect app, a single member of staff getting it would need thousands of people tested, the number of false positives would likely just make people not use the app.

though I guess some measure of "time spent" and "riskiness" could be worked out eventually... eg, it would alert other employees to get tested, but maybe only tell customers to keep an eye out for symptoms. but how would the app know you were in tesco and not in someones flat above it.
permalink time spent in the general location,
how much you moved about? any flat is going to be smaller than the floorplan of a supermarket. however, visiting a friend that lives over a corner shop would be harder to differentiate
permalink I guess it they are working on bluetooth like the
apple one it's probably easier... but that doesn't track geographical data so less useful to pick up problem locations.

block of flats would seem a problem for anything that relies on GPS.