Familiarity appears to be a key element of a successful advertising campaign, as the first screening of the Coca-Cola Christmas advert that remains unchanged each year attracted the greatest emotional engagement of the festive ad premiere season.

This is according to research carried out by Realeyes, which used artificial intelligence technology to measure people's reactions to Christmas advert premieres.

This year, the Coca-Cola ad was shown slightly differently, with the families from Channel 4's Gogglebox shown reacting to the advert as it played, which suggests that familiarity and being able to share an ad-viewing experience with others are important elements of a successful campaign.

Vodafone's 'A Christmas Love Story' ad was ranked as the second most engaging, followed by McDonald's 'Carrot Stick Christmas' advert.

Despite being the 'brand leader' in the Christmas ad space, John Lewis only ranked 17th on the list with it's 'Moz the Monster' campaign.

Mihkel Jaatma, chief executive of Realeyes, commented: "This year saw advertisers trying to be more authentic by using real-life situations, humour and romance to relate to people, which could be seen as a way to cheer them up via universal themes after what's been another divisive and turbulent year."