The ad scored just one star out of a possible 5.9 maximum across nat rep, Labour voters, Conservative voters, other voters, and the ‘undecideds’.

Labour’s ‘It’s Time for Change’ ad performed only slightly better, scoring two stars on nat rep, but hit 5.1 amongst Labour voters.

System1’s creative effectiveness testing involved asking audiences how they felt about the adverts, to determine people’s emotional response to the advertising stimulus they are exposed to. It is designed to reflect not what people say about how they intend to vote, but how they feel.

The research also tested how voters feel about each party’s leaders, with Rishi Sunak making voters feel the least happy out of all leading politicians.

Rishi Sunak and Labour leader Keir Starmer are equally well known, the testing found, but Sunak generates the least amount of happiness among leading UK politicians ( 16%) and highest amount of negativity ( 50%). This is compared to 23% happiness and 28% negative emotion for Starmer. 

Johnson achieved a 23% happiness score, a figure rising to 59% among Tory supporters, compared to 49% for Sunak.

Nick Williamson, marketing director at System1, said: “Our testing shows the Tories are in serious trouble across the board. Not only are they failing to inspire the must-win cohort of floating voters, but their ‘Start Saving’ creative fell completely flat, even amongst their own supporters.

“The controversial ‘winner’ of our testing is Boris. His brand still burns brightly, as he generates more happiness among decided and undecided voters than both the unpopular PM and bland PM-in-waiting.”