Boris Johnson will on Thursday promise voters in the South that his flagship strategy to "level up" the nation will not make them poorer.

Mr Johnson will frame his vision to boost the North and the Midlands as beneficial for all regions, relieving pressure on the "overheated" South.

In a landmark speech in the West Midlands, he will insist that "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".

It comes in the wake of the Tories’ shock by-election defeat in Chesham and Amersham last month.

A Conservative majority of more than 16,200 was overturned by the Liberal Democrats, in part due to a revolt against the Government’s controversial planning reforms aimed at meeting a pledge to build 300,000 new homes a year.

There are also concerns in the Tory shires over the Government’s emphasis on boosting transport links, infrastructure and business investment in the North and the Midlands.

In a message designed to soothe the party faithful ahead of the autumn publication of a White Paper on "levelling up", Mr Johnson will say: "We don’t want to decapitate the tall poppies. We don’t think you can make the poor parts of the country richer by making the rich parts poorer."

In a swipe at predecessors Theresa May and David Cameron, as well as former Labour administrations, the Prime Minister will accuse previous governments of having channelled investment too heavily into areas "where house prices are already sky high and where transport is already congested".

The result of "turbo-charging" London and the South-East has been to drive property prices even higher and "force more and more people to move to the same expensive areas", he will say, leading to southerners facing longer commutes and having less leisure time to spend with their families.

"They worry at the same time that the younger generation won’t be able to get a home and that their leafy suburb or village will be engulfed by new housing development, but without the infrastructure to go with it," Mr Johnson will add.

He will say that progress in "levelling up" will have been made by the Government "when we have begun to raise living standards, spread opportunity, improved our public services and restored people’s sense of pride in their community".