So the government's plan to have internet service providers turn off your access to "adult" sites by default is going well, as it emerges that sexual health and sex education sites are being blocked while some hardcore porn outlets are not.

An investigation carried out by the BBC found that all four of the major ISPs who have rolled out filters (BT, Virgin, Sky and TalkTalk) found that what qualifies as "pornographic" varies hugely from ISP to ISP.

Some services halted access to rape and sexual abuse help centres, porn addiction sites and sex education hubs while failing to block 100% of actual adult content.

In-n-out

The porn blocks are opt-in or -out, so you have the option to either have the "parental controls" in place, or say "no thank you, I would like unfettered access to the internet."

While the idea behind the block may be sound, there are many issues with ISP-level filtering of what you can and can't see on the web.

Critics of the scheme worry that the government could eventually force ISPs to block other kinds of websites - like, say, those that push an agenda counter to the one endorsed by the government itself, at which point "filtering" becomes "censorship".

In the short term, people with sex addictions and those who have been abused face a harder time getting anonymised help online, while even accidentally reducing access to sex education, which can help reduce unwanted pregnancies, spread of STDs and promote healthy attitudes towards sex, seems counterintuitive.

TalkTalk, Sky and BT all conceded that the filtering tech is not 100% perfect and that their algorithms and tools are constantly being updated.

Sky said that it has a "quick and easy way for misclassified sites to be unblocked", BT pushed its customisation tools and TalkTalk lamented the lack of "silver bullet when it comes to internet safety".