Herbert, who owns a chain of 60 Kentucky Fried Chicken outlets in Northern Ireland and Scotland, and McCormack, a former shareholder in off-licence chain Winemark, are already among the wealthiest business people in the North. Their quick flip on the Scottish shopping centre has netted them another 30m.

The duo's investment vehicle, Donegall Place Investments, bought the St James Centre, dubbed "one of the ugliest buildings in Scotland" by Edinburgh city council, for 238m in December.

Michael Hopkins of McKibbin Commercial Property Services in Belfast, which managed the property for Donegall Place, said the building had not been put up for sale and that the offer to buy it had been unsolicited.

"We had a three-year plan to refurbish the centre, to let the vacant space in it and to put in a food court and things like that, " he said.

That plan changed, however, when Donegall received a call from Henderson UK Shopping Centre Fund, a retail property fund run by asset manager Henderson Global Investors.

"There was enough money for us to go, so we left, " said Hopkins.

Henderson, which has also bought an office building adjoining the shopping centre, has plans for an extensive mixed-use development on the site.