I did email a isp a while back asking them would they make me liable if I couldnt keep my FTTP for 2 years due to tenancy expiring on property, at first they refused to talk unless I gave them an active FTTP postcode, so gave them a postcode, then I got a response along the lines of our supplier requires us to commit this long so I would be liable, I then linked them some documents from openreach stating thats not true (1 month) and they stopped responding.
Its a shame plusnet a budget ISP has no 12 month packages.