Seven major English cities, mostly in the North, are to challenge the government to stop Britain's economic map becoming "structurally unbalanced."

A high-powered conference in Sheffield will warn Whitehall "overheating" in the South East is threatening UK economic growth as a whole.

The second Core Cities summit - comprising Manchester, Liverpool, Newcastle, Sheffield, Leeds, Birmingham and Bristol, meets in Sheffield on Thursday.

The seven cities sank traditional municipal rivalries and launched a united campaign last year for a bigger slice of the nation's wealth to be shared among the regions.

The strategy is based on the success of European regional cities such as Lyons in France and Stuttgart in Germany, both of which compare favourably with their capital cities.

"Economic growth in London and the South East has attracted a population inflow which is creating pressures on land, housing and transport," says a paper being published ahead of this year's Core Cities conference.

Branch office economies

The paper, produced by Hugh Sharp, Economic Adviser to Sheffield City Council, says migration from our leading cities is creating in many areas a surplus of housing and unused land, a run-down environment and the social consequences which flow from entrenched unemployment.

The result, he says, will be doubly unpalatable. Increasing congestion will throttle the potential for growth in London and the South East and the regions will increasingly become "branch office economies".

It is a different story across the Channel, says Mr Sharp. Gross domestic product comparisons show many continental city-regions to be much more prosperous than the main UK city-regions outside London.