Incredible story in The Times, which I'm told is definitely true. For most of its existence, the contact tracing app for England and Wales has been using the wrong risk threshold, so it's hardly been sending out any alerts telling people to self-isolate
thetimes.co.uk/article/softwa…
thetimes.co.uk/article/softwa…
One of the biggest complaints about the app has been ghost messages saying "you've been near someone with covid-19". If the risk threshold hadn't been artificially high, many of those alerts would have been instructions to isolate
As it was, people were told to ignore them
As it was, people were told to ignore them
The Times has described this as a software bungle. I understand the issue was incredibly human. There was meant to be a change to the risk threshold on the app, but no-one went in and made the update
One slight quibble. Test and Trace can't say how many people have been told to isolate by the app, because the privacy protections don't give them access to that information. I'm told they do model this though, and they could put that out... 
Sorry, Sunday Times, not Times! Full credit to its excellent reporters @Gabriel_Pogrund and @TomCalver2
Bit more on this. For proof that the app's risk threshold should have been changed pre-launch - and that DHSC and Test and Trace thought it had been changed - take a look at the archived version of the algorithm FAQ web.archive.org/web/2020100308…
This paragraph has since been deleted
This paragraph has since been deleted
Statement from DHSC. Worth emphasising that is a failure of omission: no-one has been falsely told to isolate as a result of this error. If you're thinking about downloading the app, nothing in this story should give you pause
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