I remember hearing George Formby exclaim "Well I'll go to the foot of our stairs!" in at least one of his comedy films - possibly 'Leave it to George' , or 'No Limit'. (For those who don't remember/never heard of George, he was a famous comedian from Lancashire, who died around 1960.)

A quick Google search produced this answer:

http://www.phrases.org.uk/bulletin_board/38/messages/1425.html

and this one:

http://uk.answers.yahoo.com/question/index?qid=20090506115327AAxdKGE

The latter also attributes the phrase to Tommy Handley - apparently used on the 1940s radio comedy show 'ITMA'.

And that's all I know folks,

Wassail!