Boris Johnson has conceded he offered the “skeleton” of plans to level up the nation when he proposed greater regional devolution in a speech billed as a major bid to define his vision for the UK.

The Prime Minister suggested county leaders could possibly get fresh powers and reiterated plans for investment on infrastructure, education and regeneration, but offered few new details for his great ambition.

He promised that boosting the North will not be to the detriment of the South, as he tried to keep traditional Tory voters onside while courting former Labour supporters in the North and Midlands.

Labour leader Sir Keir Starmer dismissed the speech as “all soundbites and no substance”.

One new proposal in the speech at the UK Battery Industrialisation Centre in Coventry on Thursday was to “rewrite the rule book” to take a “more flexible approach to devolution” in England.

We need to rewrite the rulebook with new deals for the counties

He said local leaders in towns should be “given the tools to make things happen for their communities”.

“To do that we must take a more flexible approach to devolution in England,” Mr Johnson said.

“We need to rewrite the rulebook with new deals for the counties and there is no reason why our great counties cannot benefit from the same powers we’ve devolved to city leaders.”

But he cautioned “we must get the right local leadership” so there cannot be a “one size fits all template”, as he criticised the “loony left”.

“One possibility is a directly elected mayor for individual counties. And if you can think of a better title than mayor for somebody who represents a county then please send me an email,” he added.

In a press conference during which he was challenged on allegations that his past remarks have given a green light for online racism, he was asked where his clear strategy for levelling up is.

“I am respectfully going to urge you to just go back over some of what I said because I do think that in all fairness there was at least the skeleton of what to do,” Mr Johnson responded.

No 10 said that new “county deals” will potentially allow more areas to “benefit from strong, high-profile local champions”.

A levelling-up policy paper is expected to be published in the autumn, where more detail should be fleshed out.

Mr Johnson described his levelling-up vision as an attempt to fix the UK’s “unbalanced economy”, which he said means “for too many people geography turns out to be destiny”.

He reiterated commitments to rolling out gigabit broadband, investing in rail and roads, giving the guarantee of “great education” to all children, and boosting funding for science and technology and tackling crime.

Brexit received just one mention, with a pledge to create jobs by using new freedoms such as the ability to build freeports.

The Prime Minister sought to ease the jitters of some Conservative MPs by promising his agenda would not mean “levelling down” wealthier areas, in the wake of the loss of the former safe seat of Chesham and Amersham in last month’s by-election.

Having secured his place in No 10 by winning over traditional Labour voters to make massive gains for the Conservatives in the north of England and the Midlands, Mr Johnson argued “greater regional prosperity means more customers and more business for our national metropolis”.

He said: “Levelling up is not a jam-spreading operation, it’s not robbing Peter to pay Paul, it’s not zero sum – it’s win-win for the whole United Kingdom.

After some England players were subjected to racist abuse, the Prime Minister was forced to defend himself from criticism over his past remarks as well as his, and Home Secretary Priti Patel’s, responses to the team being booed for taking the knee.

He said he is sorry for the “things that I have said that have caused offence and continue to apologise for them”, and he pledged “practical steps to stamp out racism”.

Sir Keir said the Prime Minister had failed to set out a coherent regional strategy in his address.

“It is all sound bites and no substance. He promises jam tomorrow – that is what this Prime Minister does – but there is no delivery,” he said.

Deputy Labour leader Angela Rayner added: “Boris Johnson – the actual Prime Minister – in a speech that was supposed to set out his policies to address regional inequality, asked the public to email him with ideas.”

Mr Johnson’s former aide Dominic Cummings dismissed the speech as a “joke” and said “levelling up” was a “vacuous slogan” that people did not understand.

Local Government Association chairman James Jamieson said now is the “right time to bring forward an ambitious new devolution settlement”.

“We support the Prime Minister’s refreshed commitment to turbo-charge this agenda and we look forward to working with councils and government to make this ambition a reality,” he added.

Confederation of British Industry director-general Tony Danker welcomed the commitment to greater regional devolution.

“The PM is right to recognise the importance of creating confidence among businesses to invest, and empowering local leaders to deliver,” he said.

“For too long, we have been so much more regionally unequal than our economic competitors.”

But TUC general secretary Frances O’Grady said the Prime Minister must move on from “empty sound bites”.

“There has been precious little to show for the Government’s vaunted levelling up agenda, and today’s speech will do little to change that,” she said.