St John's Ambulance 'popcorn' by BBH

The ad, directed by Jeff Labbe, shows a family eating popcorn at home, until one of the children appears to choke.

The mother looks straight into the lens and cries out to the unsuspecting cinema audience for help, which prompts the actress to stand up run behind the screen, appear in the ad, and then reappear in the cinema.

Screened last week in association with DCM and Cineworld Haymarket, the campaign is also seeded online, has a Facebook page and a Twitter feed.