Boris Johnson’s flagship “levelling up” speech has been criticised by experts for containing scant new policy as concern grows among Conservative MPs that the guiding principle of his premiership risks becoming little more than a soundbite.

Two years after first committing to levelling up, the prime minister travelled to Coventry to deliver a freewheeling speech heavy on rhetorical flourishes but light on detail, and urged local leaders to send in their own suggestions.

Thinktanks including the Institute for Fiscal Studies and IPPR North said it contained nothing new and that it was time for “deeds not words”.

Despite Johnson’s levelling up adviser, the Harborough MP Neil O’Brien, being well liked, some MPs are beginning to worry about whether the plans have any substance.

The Conservative MP Laura Farris told the BBC on Thursday that levelling up was an ambiguous phrase that “means whatever anyone wants it to mean”, and a former cabinet minister said of the speech: “He seems to be throwing the kitchen sink at it, which suggests there isn’t much of a coherent idea behind it.”

Johnson said in his speech that strong leadership was “the yeast that lifts the whole mattress of dough, the magic sauce, the ketchup of catch-up” and suggested he would like to see more local mayors, perhaps at the county level. He then appeared to say he would not want to devolve too much power in case the “loony left” took charge.

“Of course, you can see the risk and the catch in all this. We have to learn lessons of the last 50 years. Ken Livingstone of the 2000s was a very different creature from Ken Livingstone of the 1980s, but the loony left remains pretty loony and we need accountability,” he said.

He called for more “county deals” to devolve power to local areas, which he said would not be “one size fits all”. Several county devolution deals already exist. The communities secretary, Robert Jenrick, separately announced 15 more town deals on Thursday to fund high street regeneration.

Johnson also reiterated a string of existing government policies, many of which apply across the UK, including hiring new nurses and boosting the science budget, and he sought to reassure southern MPs anxious that their voters are being forgotten that levelling up applies across the country.

More policies for levelling up are expected in a white paper on the subject in the autumn, but experts criticised the speech for failing to address the problems of inequality and economic imbalances that Johnson set out, and for contradicting other government policies.

Erica Roscoe, a senior research fellow at IPPR North, said: “Boris Johnson promised to ‘level up’ the country in his first speech as prime minister. It was welcome rhetoric, but two years on our deep divides between and within regions are growing, and places like the north are still waiting for the powers, resources, and transparency they need to see from government to level up for themselves.

“The need for deeds, not words, has never been more urgent.”

Torsten Bell, the director of the Resolution Foundation, said: “The speech was light on new ‘levelling up’ policies, but much more of a problem is that the government already has a big levelling down policy – the £20 a week cut to universal credit. One in three households in the Midlands and the north will lose £1,000 a year, compared to one in five in the south-east.”

Paul Johnson, the director of the Institute for Fiscal Studies, said: “There’s nothing new, either about the diagnosis or the fact that you need to do something about it, or about anything that’s been said.” Devolution may well be part of the solution to the UK’s imbalanced economy but “the fundamental issue is jobs and skills”, he said.

The Coventry South MP, Zarah Sultana, said: “Boris Johnson came to Coventry today to talk about ‘levelling-up’ but he’s not fooling anyone. It’s a meaningless soundbite, totally at odds with his record in office. His party has overseen 11 years of managed decline and levelling down“Johnson didn’t even bother to mention Coventry once in his speech.”

The prime minister’s hostile former adviser Dominic Cummings wrote on his blog that levelling up was “just a vacuous slogan” that Johnson had come up with “partly out of irritation with being told to focus on the core message in 2019 and partly because he was irritated with people calling him a puppet who repeats my slogans”.