just done a quick check on
www.webwise.net, a.webwise.net and
www.oix.com
admittedly these aren't confirmed as the domains that the opt-in/out cookie will be tied to, but bear with me
these 2 domains are not in BT's or VM's net block (it's fasthosts if you care)...
which means that if you visit any site (the guardian for instance) that is in oix, then the cookie will be read from somewhere outside BT or VM.. which is in direct contradiction to what we've been spun.. i.e. no data will go outside the ISP..
the cookie can be read by one of these sites then who knows.. your unique oix id and browsing habits, can now be strung together with your ip address and anything else your browser wants to give up..
edit : sorry for mentioning BT but i don't think this is a purely cable problem