Are You Sitting Comfortably Then I'll Begin

The teaser at the end of tonight’s Doctor Who for next week’s episode, The Idiot’s Lantern, included Maureen Lipman uttering the immortal line from Listen with Mother of "Are you sitting comfortably then I’ll begin". The Doctor used a bit of it at the start of the episode School Reunion. Are they just teasing the rest of the world, giving those of us who grew up between 1950 and 1982 a little cultural reference or is there something more to it all? Enquiring minds want to know.