[FuzzyDunlop]

This already happens on Giff-Gaff (a mobile network) and is opt-out only. It's not uncommon to find out a security-related blog on the front page of HN is blocked by the filter, and sites for projects like Metasploit are also blocked.

It's silly.

[blueskin_]

All mobile networks have this censorship, but it was easy to opt out of, and the censorship is very sloppily implemented (for me, changing DNS servers or using any trivial proxy bypassed it before I opted out).