I would be very surprised if Apple and Facebook (and Google, with GMail, GTalk, Hangouts, etc) didn't use this golden opportunity to swing their weight about and assert who's really in charge of technology around here, by simply wholesale blocking use of all their communication tools in the UK to comply with the law.

I have a feeling that if they did this, the uproar would be sufficient to have the law reversed by emergency measures.

If they were followed, as they may well be, by a whole host of other essential internet services (Google Search, Wikipedia, Github, etc etc etc) just switching off simultaneously in the UK on the day the law comes into force, that might be sufficient to ensure this sort of dumb shit is never done again. The cost of billions of pounds of lost productivity would probably ensure that.