The political consultancy Cambridge Analytica claimed that it used a similar technique, known as psychographics, in its work, though it has denied using data sourced from a Facebook personality quiz in the 2016 US presidential election.

Facebook's patent says potential sources of data could include "status updates, notes, messages, posts, comments, or any other communications from which linguistic data may be extracted".

It says the personality characteristics could then be stored in a user's profile and used "to select news stories, advertisements, or recommendations of actions presented to the user".

Prof Eckles told the BBC that his research had involved asking Facebook users to complete surveys that posed personality questions, adding that it had been made clear that the social network was behind the questionnaires.

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He acknowledged that "psychographic [advertising] targeting raises some distinctive ethical concerns" but said he was doubtful it would ever have been effective.