I googled (via mobile since BT are blocking me from using my own broadband) and found that "BT Parental Controls" and "BT Protect" cause this. I have not opted into either of these, but I tried to follow the instructions to disable them in case some bug on BT's side had opted me in.
There is no "My Extras" section or "Personalise your settings" button in "My BT" for me and no "My Security" section either. When I follow any links relating to "extras", I only get telephone options ("BT Smart Talk", "BT Call Protect").
When I try to access insecure HTTP sites, BT hijacks the request and I see the following:
You are seeing this page because you are using a BT service which requires the use of BT DNS Servers and it appears that you are attempting to connect using a DNS server outside of our network.
Our BT Web Protect and BT Parental Controls services both require the use of our BT DNS to keep you safe online.
You may have selected a different server in your network settings or installed an application that uses an alternative service.
Click here to find out how to fix this
To turn off BT Protect or to delete Parental Controls, log in to www.bt.com/mysecurityhub
But when I click the link at the end, I get the following:
Services not found
This account does not have any My Security extras
Select another account or go to My BT to manage this account.
How do I disable BT Protect, BT Parental Controls, and any other BT hijacking "extras", given that none of them appear in "My BT"?
Re: DNS hijacked by BT, and "parental controls" and "protect" do not appear for
I used BT's online chat and they were certain that nothing was wrong with the network despite my proven hijacked DNS (and also the missing options in "My BT", which are probably not "network"-related). They then told me to use "tech experts", which costs £8/month.
I design networks and communications infrastructure for a living (the most recent of which included a satellite) so I'm quite familiar with network protocols, diagnostics, etc.
Basically, they want me to pay more on top of what I'm already paying for BT Infinity, in order to remove some malicious "extra" that I'd never asked for in the first place.