The filtering is almost certainly applied on the ISP end, with a web interface to a control panel.

I have no idea what Cameron means when he says it will be on all new computers by the end of the year, but he mentioned iPads. I suspect it's just his confusion about client / server, and that the OS will have no effect.

Yeah, I suggested as much but loose politician lips can sink ships. Especially ignorant ones. A poorly drafted law can have unpredictable consequences and later be impossible to change with the "My opponent wants your kid to be sodomized on the internet by copyright pirate, terrorist, porn industry magnates, blasphemers,{scary moral panic subculture of the month}" argument.