The initial trails later this month only involve testing before and after the events, as the app won't be ready.
A lot will depend on what the results of the tests show.
If the trial events go ahead, and the testing shows that there is little or no transmission of the virus, then it is going to be much more difficult to persuade people that COVID status certification via the app is necessary. You may find the compulsory COVID status certification is limited to certain mass participation events that people would normally book in advance for, and not the sort of things that people do on a regular basis.
I really hope these don't come in as once they come in, they will be very difficult to get rid of. Also, given this government's record, they won't be out until next year, be described as 'world-beating' and not actually work.
Though I do think they are basically inevitable for international travel.
The longer it is before the app is released for general use, the less reason there will be for using it.
If it doesn't beocme available until the end of the year, then we will have had six months worth of figures with most things being open, and unless there is a large increases in cases and hospitalisations as a consequence of all the lockdown easings, then what is the point of having an app for COVID Status Certification?