The traffic light Smart Phone App is a great idea.
But sadly the The NHS contact tracing app will be a heap of krap and will not work properly. For it to work, it has to be the front open application and not running in the background. But people don’t use their phones like that, so the app will only collect data intermittently. Data needs to be collected all the time, in the background, and the NHS App doesn’t do that.
Germany and France who were ahead of us have already abandoned their own apps are are now working closely with the Google-Apple collaboration (GA). GA have addressed and solved the privacy concerns, will be built into the iOS and Android Operating systems. A third party app produced for Governments will never be as good as Google’s and Apple’s engineers combined effort.