UK to "encourage" Apple and Google to put nudity-blocking systems on phones

Indeed. But this already has happened for most people. All non-jailbroken iphones and most Androids cannot have their bootloader unlocked, and even if they can, the stuff you can run is often still substantially controlled by Google.

Though in theory this can also be done without involving the OS at the device driver level. It's not hard to imagine a CNN running inside your display controller to detect a bbox and blur out the nudity. It'd still suck and be a middle finger to the owner, but I don't feel like this is much worse than what's already there. Given the popularity of porn, I can easily imagine this sparking a general public sentiment against all this nonsense.