I came across this site, which provides a system designed for small guest houses and coffee shops:
http://hotspotsystem.com/hotspot-software
They offer instructions for using a range of routers that can be configured to divert to a splash page for guest login. They also sell routers with their own version of OpenWRT which are plug and play. Their support suggests it's as easy as hardwiring their router to my BT Hub, configuring their router with the kinds of restrictions I want, then off we go.
Can anyone see any obvious pitfalls with this approach? I'm tempted by their modified TP Link WR841N unit. I don't need lots of range or capacity.
I really need to do something, last night two of my guests seem to have had their phones set for some kind of cloud backup. They uploaded almost 2GB between them, and that was just in the couple of hours I let them on the network. On a slow ADSL with 448k upload that's a big deal.