Unfortunately there are tens of alternate domains (e.g. thisproxykillscensors.uk with a new one launching every week (£4 for a .uk + an API == war of attrition) ) and ~15 servers running the squid backend rotated each month (got to love cloud automation) and the PAC file takes randomisation arguments.
Apologies for making your lives more difficult but state coerced national censorship is dangerous and needs to die.
edit: In a few weeks the BGP filtering will go live and will restrict the proxies to subnets announced by BT, Virgin, TalkTak, Sky and the mobile providers. If your IP blocks aren't announced by those ASNs the proxies won't allow connections
