BT's new network-level nudie no-no filter system will block access to sites promoting proxies and anonymisers, The Register has learned.

However, the one-time national telco has insisted that it won't choke VPN connections over its network now that its Parental Controls service, using DNS lookup technology, is in place.

On Friday, BT flicked the switch on its promised system to supposedly help to protect kids in the UK from sex/drugs/violence/etc online, in the hope of preventing regulatory meddling from Whitehall.

New subscribers will be forced to opt-out of BT's censorship machine, while existing customers will be nagged to switch on the system early next year.

Redwood, California-based Nominum, whose chief scientist is Paul Mockapetris - inventor of the Domain Name System - is helping to "determine which content to block," a BT spokesman told El Reg.

"The categorisations are constantly updated to keep pace with the evolving content on the internet," he added.

Parental Controls, we're told, will not be applied to connections made over Virtual Private Networks. But, here's the fun bit:

The filter "doesn't block VPN connections, but does prevent access to sites promoting the use of proxies and annonymisers [sic]," the BT spokesman said.

Some IP addresses will be blocked "where required", he added, which we presume relates to - among other things - court orders that demand ISPs to block access to sites serving up links and torrents to copyrighted material, even though there are obvious workarounds.

Rights-holders in Britain can now use legislation to force telcos to filter out sites that infringe their copyright, following a landmark ruling in 2011. They can also regularly dictate to ISPs what IP addresses and URLs should be blocked, as well as including on that list proxies which simply link to that unlawful content. ®