I think smartphone based contact tracing and notification that uses actual geolocation might well work, but the whole advantage of the minimally disclosive smartphone apps based on BT radio was that they didn't share your every movement with big brother.

There seem to broadly have been three schools of thought:

1) Because of how radio propagation works, BT based contact tracing simply will not work.

2) BT based contact tracing will work but if Apple/Google don't support it through special permissions / an API then it will not work in practice.

3a) BT based contact tracing will work and workarounds can be designed even without phone OEM special treatment.

3b) Phone OEMs can be pressured to support our app.

NHSX was either in camp 3a or 3b, their view was that without certain characteristics that neither Apple nor Google were willing to support, it wouldn't be particularly useful. We don't know whether they genuinely thought they might be able to change the OEM's minds about this or whether they thought they could get their (admittedly very clever) system of ping pong keepalive signals to work. Incidentally, in lab and controlled conditions, it did work. If you switch on the app on your iphone and then walk into a crowd, it works. That's because there will be enough android devices around to ping your app into life. The problem is that if you switch the app on at home, walk down an empty street to your train station, and then get on the train, the app will have backgrounded already by the time you're back in BT range of an android device. This is the kind of thing where it is really easy to say ahead of time that it isn't likely to work but impossible to know for sure.

Many others here on HN were in camp 2. They believed that BT contact notification was possible and useful but that in practice, it would not be possible to make it work on iphones without special treatment from Apple. That has proved correct.

However it may be the case that in everyone's collective excitement, not enough people listened to RF engineers in camp 1. I think it was easy for people without much RF experience to think that while this would be an obstacle, it was still much better than nothing.

It now looks like they were indeed right, in a very wide class of enclosed space situations like buses, it just doesn't work at all. Once you remove public transport (I assume trains will have the same issue) as a use class, why does this even add anything to human contact tracing? Since in many places we are already requiring all restaurants and bars to keep contact details for every person in a party, that seems well covered. Most other interactions will be subject to traditional contact tracing.

Additionally it seems (and this may be UK specific, but I bet not) that one of the outcomes of the Isle of Wight trial was that people really did not like finding out that they would have to self isolate for 14 days from an app notification. It just doesn't have the gravitas of a human being calling and asking you to do it. I have to admit that I would not have guessed that. I suspect I share some personality traits with other HN users in that I would not in fact mind receiving that information from an app.