The expression "I'll go to the foot of our stairs" is used to express surprise. It is a form of exclamation. Similar ones would be "Stone the crows!" (a bit old-fashioned, no doubt) or "Christopher Columbus!" (ditto), or the more common "Jesus Christ!" There is no problem with the meaning, by which I mean the way it is used. I have found that it is mostly Northern English, and more particularly related to Yorkshire. Apparently, it is still in use. It is frequently featured in sitcoms etc when there is a typical Yorkshire character, in order to add a bit of local 'colour'. No one seems to know where the expression comes from. Why: "Go to the foot of (the stairs)"? Why would it come into it at all, when expressing surprise? Or is this one of those deliberately absurd phrases used in a tongue-in-cheek way? "Our" seems to imply the person is talking about his or her family-home. Suggestions welcome.