In recent speeches, Boris Johnson has cited Kermit the frog and James Bond, and drawn up on all manner of football analogies. Yet none of them were as widely panned as the one he gave to business leaders earlier this week, when he went on a long – and seemingly unscripted – riff about Peppa Pig.

According to political scientists, the furore is a sign that cracks are beginning to show in his freewheeling political style.

While they (mostly) admired the way he has always got his message across, they said the criticism suggested people were beginning to tire of the crisis-mode boosterism that felt appropriate for the early stages of the pandemic.

It’s not that Johnson’s speech to the CBI on Monday was particularly different from ones he has given before. But this time it was widely criticised as “shambolic”, “a mess” and the “most embarrassing by a Conservative prime minister”.

Experts who spoke to the Guardian said that rather than a departure in style, the speech could represent a point at which voters were no longer amused by his jokes, in a new chapter of his premiership.

Michael Kenny, the director of the Bennett Institute for Public Policy at the University of Cambridge, said the CBI speech was a “car crash”. “As the political context changes, the big question for him is whether that mode of speaking needs to adjust.

“His boosterism – relentless optimism and inflationary rhetoric about what the government is doing – works better in a position of political strength, not when you’re under huge pressure and there are lots of obvious problems people are starting to worry about. The risk is you look disconnected and almost avoidant.”

Yet Johnson’s speeches have been a cornerstone of his “unique” political style, which draws on comedy and the performing arts. This had made him “the first true celebrity prime minister in British political history”, said Matthew Flinders, a politics professor at Sheffield University.

“He’s absolutely fantastic in terms of his performative skills and his ability to work a crowd. He uses speeches not to convey information, but as a tool of entertainment, to ingratiate himself and develop himself as a character.”

This use of humour also enabled him to control the conversation through deflection, Flinders said. “His most famous tactic is you ask him a serious question, he’ll respond with a story that will evolve into a joke, and by the time you’ve heard that, you’ve forgotten the original question.”

The political scientists agreed Johnson’s style formed part of a broader trend towards a more informal way of doing politics that rejected the technocratic professionalism of the 1990s.

Steven Fielding, a political history professor at the University of Nottingham, said the way Johnson’s speeches drummed in clear messages – such as “get Brexit done” – were a better fit for today’s “attention deficit culture” than the more complicated political arguments of the past.

Academics specialising in linguistic analysis said Johnson’s speeches showed a distinctive use of language. Helen Thaventhiran, a lecturer in the philosophy of language at the University of Cambridge, said he used many of the “stylistic tricks” of populism, for instance his reliance on everyday language, slogans, anecdotes and jokes.

“You think you’re getting something that makes you feel full or satisfied. You remember the ‘Picasso-like hairdryer’ [as Johnson described Peppa Pig’s appearance], but you’re not really getting anything nutritious, you’re not getting policy or logical thinking.”

Dai George, a UCL researcher specialising in syntax, said that unusually, sentences in Johnson’s transcribed speeches were “broken and scattered”. “This allows a more complex syntax to land with the punch of a tabloid soundbite.”

George added that while usually Johnson’s analogies were well received thanks to their “imagistic flair or a cognitive spark of surprise”, the Peppa Pig story failed because it resembled a “boorish anecdote from a best man speech”.

Zahira Jaser, an assistant professor at Sussex University who specialises in the psychology of leadership, suspected the CBI speech might also not have succeeded due to the audience.

Whereas during his much-lauded Conservative party conference speech Johnson was able to take a more natural position as a “heroic leader” through classical references and grandiose statements, at the CBI “the people in front of him will be persuaded by numbers, and he finds it much more difficult to reason in numbers than in words”, she said.