No it isn't. That is an optional opt in feature available to customers of O2. A customer has to explicitly opt for the Under 12 filter to be applied to their account. O2 do have an adult content filter that is enabled by default (which requires identity verification to disable) but that does not block access to tech and civil liberty websites, it blocks access to pornography, it is not what this article talks about. There are 2 filters, adult content (default on O2 accounts), U12 (opt in). This article uses the filter status of websites on the U12 list (a whitelist) that has existed for many years and has nothing to do with the government as evidence that the government filter is oppressing children. They have no connection.
I get it, this country wide opt-out filter requirement is bad and it shouldn't be happening, I agree, but whining about something that has nothing to do with it makes absolutely no sense. The O2 U12 filter is fundamentally different, it's an optional extra customers can opt in to. This article has nothing to do with the "porn filter". Nothing!