This assumes that most Britons oppose their government having such powers.
Which maybe they do in abstract, but when the government reframes this as, "Apple prevents us from catching child abusers", I don't think Apple would win that match.
That still presumes that as an entire voting population, Britons would choose freedom over convenience or perception of propriety. The current government there doesn't appear to reflect the former.
I don't think "people" are going to have a say in this at all. Their privacy is now between Apple and the UK government, two entities with less-than-favorable track records protecting their constituents.
The UK could have followed the EU's lead in forcing Apple to diversify their service offerings. They could have written their own consumer protection laws or leveled lawsuits about Apple's dubious privacy considerations whenever they wanted. But instead they waited until it was too late, because everyone thought; it would never happen to me, right?
I know people will call this a fatalist reaction, but Apple has fought hard to control their fate. Now you have to trust that Apple will do the right thing, while Tim Cook stands shoulder-to-shoulder with America's most radical leader in half a century. If this matters to Britons, they should vote with their wallets and ditch Apple themselves.
Which maybe they do in abstract, but when the government reframes this as, "Apple prevents us from catching child abusers", I don't think Apple would win that match.