The campaign's "save the boy" TV spot airs tonight (16 September) and accompanies an interactive web video.
The ad opens with a father and son playing football, and what is presumed to be the mother looking on from a kitchen window. When the father is distracted by a phone call the boy climbs a tree, falls and is knocked unconscious.
The voiceover describes how the woman in the kitchen is a St John Ambulance volunteer. As she rushes into the garden it is revealed that she has no connection to the young boy and is only hurrying to get her washing out of the rain.
The spot closes with the young boy and his distressed father alone in a park.
The TV spot directs viewers to St John Ambulance's website where an interactive video explains how to administer first aid.
St John Ambulance based the campaign on research that found 55 per cent of parents lacked life-saving first aid skills.
The ad was by Bartle Bogle Hegarty, which was handed St John Ambulance's creative account without a pitch in 2008.
Rob Ellis and Alex Ball created the TV spot, which was directed by Dougal Wilson – who has also made ads for John Lewis and Three – through Blink. Mobile agency Monterosa, which was acquired by BBH earlier this year, built the interactive website.
John Ayling & Associates handled the media planning and buying, while St John Ambulance’s in-house team and GolinHarris arranged the PR and social media aspects of the campaign.
Sue Killen, the chief executive of St John Ambulance, said: "Unfortunately, our volunteers can’t be everywhere so we’ve developed an online experience to help more people be the difference between a life lost and a life saved.
"We don’t want anyone to be helpless in a first aid situation especially when learning life saving skills is so simple."
BBH's previous campaign for St John Ambulance, called "helpless", featured a man surviving cancer only to choke to death on some food at a barbeque.
The ad ran in September 2012 and received almost 150 complaints for causing distress but was not investigated by the Advertising Standards Authority as the watchdog found it was justified given its post-9pm timing restriction.