I find it very strange to see laws like this proposed. Intelligence agencies benefit the most from having end-to-end encryption mechanisms that are open source. In fact, many spies would start to die if we went back to enigma style encryption. Why? Because an NSA/GCHQ proprietary algorithm isn't safe without public scrutiny and they know it.

So when you see the alphabet agencies push against encryption, know that they don't even really want it. It's a psychological tactic to trigger you to not want to use encryption. If a law were about to pass that would have this, they would be the first lobbying against it. They just like supporting these ideas because they know it will never get there, and that many businesses such as banks will tell the government, "Okay, then you're telling us to shut our doors and end your entire economy".

BEST CASE SCENARIO is that if a country passes a law like this, all foreign countries that give internet services to that country will just stop serving that country because implementing such a system would provide criminals and hackers an easier way of breaking into their communications, and also take a large quantity of time and manpower to implement and change their current ways of working with your data. It's not even worth the effort to invest in a system that can do this sort of thing just for Google or whomever to do business with the UK.

First country to pass this law becomes the next North Korea guaranteed. Everyone pushing it knows that, too, they just want to play political mind games on the public.