It was, of course, never really about porn.

When David Cameron, egged on by the likes of the Mothers Union and ruthlessly ambitious MP Claire Perry, announced that we'd all have to make a choice about whether or not we wanted unfiltered access to the internet – with the default choice set at 'yes I do', of course – it was to prevent wide-eyed kiddies from accessing hardcore porn, we were told. No matter that tools already existed to allow parents to block unsuitable sites from their child's computer or phone if they wanted to; and no matter that all impartial research has shown that both the frequency and affect of under age viewing of adult sites is wildly exaggerated. The constant, cynical howling from the revolting Daily Mail – a ghastly, racist, homophobic and bigoted publication that any decent politician would view as extremist and toxic – ensured that our weak-minded politicians, headed by Cameron and egged on by most of the others (including Labour MPs who's only complaint is that blocking doesn't go far enough) decreed that 'something must be done'. And after displaying token resistance, the compliant ISPs have fallen into line. In the last couple of weeks, both Sky and BT has started web filtering. Virgin will follow in the new year. And the mobile phone companies have already been doing it for a long time.

And it's the mobile companies that offer a window on what we can expect. Despite Cameron's assurance that only the most pornographic sites would be blocked – he specifically stated that things like The Sun's topless Page 3 girls would not be caught by filtering – it turns out that the companies are all using their own systems, often supplied by filtering companies in the USA and China (yes, a nation that is home to companies that think a female nipple is obscene and a Communist dictatorship where free speech is virtually non-existent) and which use a simplistic, catch-all method of defining porn. And of course, it's not just 'porn' that is being restricted. Adult material was the Trojan Horse used to introduce wholesale blocking of a wide variety of content.

At the moment, only O2 actually allow anyone to check which sites are blocked under their system. You can depress yourself with it here: http://urlchecker.o2.co.uk. Naturally, Strange Things Are Happening is forbidden, listed as 'pornography' (here's a challenge – find me a single genuinely pornographic image on this site). But the last couple of days have seen the internet digging into the filters and finding that, yes, a whole load of innocuous sites are also blocked. These include Childline, The Samaritans, various sex education and domestic abuse sites, the British Library and even parliament.uk and gov.uk. Inevitably, it seems that pretty much every LGBT site is blocked.

Bizarrely, O2 have tried to blame this on the BBFC. The British censors have drawn up guidelines as to what is considered 'adult content' (you can read them here and yes, they are problematic), but they're certainly not vetting individual sites, because that would require a staff a hundred times bigger than the one they have – but 02 have been telling people on Twitter “all websites are classified by BBFC”, which suggests that either someone doesn't understand how their own system works or that someone is being rather economical with the truth. Because I can pretty much guarantee that the BBFC would not classify The Samaritans or Childline as 'adult content'. Oh, and guess what Mr Cameron? Page 3 is also blocked.

Meanwhile, BT don't allow you to look up individual sites, but have published a list of categories that will be blocked. This too caused an understandable firestorm when it revealed that one option was to block 'sex education', which included such child-corrupting things as "respect for a partner" and (of course) LGBT sites. BT have since changed the wording, but there's no evidence that they've taken any of the sites featuring this sort of content off the blocked list.

Other sites blocked include those giving “information on illegal drugs or misuse of prescription drugs” (even, presumably, those offering help to stop/avoid said misuse), nudity (which amazingly includes lingerie and swimwear), social networking, dating, games, media streaming, fashion and beauty and sites that contain profanity (which are curiously categorised as “weapons and violence”).

BT's options for blocking are heavy, moderate and light. You can turn it off entirely, though the splash page inviting you to make a choice doesn't include that option – you have to dig down deeper for that, and so most newbies will presumably think that 'light' is the most open they can choose. Very crafty, as even this bans porn, 'obscene and tasteless' (including "bathroom humour" and "frightening content"), hate and self harm, drugs, alcohol and tobacco and dating – so still reducing your internet experience to a PG rated level. At least it means that when you have that "awkward conversation with the wife" about unblocking that Cameron so relished the thought of, you can now point out that it's not porn you want to access, just a vaguely grown-up version of the web.

And of course, people have found that BT is routinely blocking sex education sites – even those specifically aimed at teens. Naturally, this will be put down to teething problems, and high profile cases will see their sites unblocked. But for every one that makes headlines, there will be ten more that don't have the clout to get the blocks lifted.

Not that this will bother Cameron or Perry, who simply wanted to be seen to be doing something and – like all politicians pushing through rushed legislation (or, in this case, merely threatening to) – don't give a damn about collateral damage along the way. And slowly, through blocking and the ghastly ATVOD – a body that requires any UK website containing video to be expensively licensed like a TV broadcaster and is using it's dubious powers to crush the UK adult industry, the British government is finally taking control of the internet. Cameron is already talking about blocking 'extremist' sites (which you can bet won't stop at Al Quada). Before long, more and more 'loopholes' will be found to be closed (how long before opting out of filtering is banned, I wonder?), more and more content seen as unsuitable for the masses and hidden from public view, more and more opinion expressed on Twitter classed as 'offensive' and so a criminal act. We're at a turning point here, and if you care at all about free speech, you will reject filtering entirely and stand up against government control of the internet and open, contrary opinion. If you think this is not your fight, think again. We all have a stake in this.

Those of you who, for whatever reason, are unable to turn off blocking - or just want to make a point - can install this Chrome extension to bypass all filters: http://goawaycameron.co.uk