NHS coronavirus app: How does contact tracing work and when can you download it? 

Well, i think even though it sounds very effective but it Itself is going to take a little longer to be effective as it requires at least 60% of adults to participate.
And people may not be that much encouraged to get engaged with this app. I Mean, who would want to be traced for 24/7? Even if they install the app they may leave the phone behind if they don't the authority to know his whereabout. In that case the app is useless.

This type of software and tracking goes well above and beyond the government's authority over its citizens. This is a slippery slope to allow tracking and communication of your device with others' and privacy will go right out the window with features like this.
Too many programs and apps already track WAY too much of our personal information, often without our knowledge, so I cannot see society willingly signing up to be tracked throughout their daily lives. Creepy comes to mind.
I would definitely not be a willing participant to constant tracking...even if I am only going out for groceries...the government does not need to know that.