John Punter, professor of urban design at Cardiff University, says separation and competition between cities is the key to improvement.

BBC: Cardiff

He insisted there would be "passionate competition" between the cities, rather than their traditional rivalry.

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Competition, he says, takes place not between nations, but rather cities.

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Still, two cities dominate when it comes to demand from foreign buyers: "The competition is really between London and New York, " Mr. Bailey says.

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