For a few years, now, I have used a cheap FON wifi access point to provide limited (internet only) access for any visitors, separate from my own wifi access.
By default, a FON device offers two networks – one private and one public. In my case the private network is POSHGAMES, which my friends use; the public FON network is one that *anybody* can log into if they have FON credentials. The good part is that by hosting FON access, you yourself gain free access to any other FON point in Europe, which also includes many BT access points.