FL310
I believe my ISP (Flyer Internet) will allow a continuous connection if you rent a modem port in additions to subscribing to the unmetered service. I don't know what the cost is, though.
Normally they disconnect after 2hrs but their site explains how renting this port will allow 24/7. Obviously this will be cheaper (& inferior to a true leased line.
http://www.flyer.co.uk/
Hope that helps,
Fujiflyer