Struggling Croydon is to be "returned to its former glory" by a £1bn plan to build Britain's biggest shopping centre.

The giant, 2.2 million sq ft mall is set to be open in Croydon's town centre before the end of the decade after a landmark agreement between London's two most powerful retail developers.

The scheme will combine the two existing malls in Croydon – The Whitgift Centre and Centrale – in one huge new scheme that will overtake Gateshead's MetroCentre to be the biggest in the country.

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The deal between the Australian developers Westfield and Hammerson, the property group that owns Brent Cross in north London, comes after a series of setbacks for what was once one of London's wealthiest suburbs and is still its biggest borough with a population of 363,000.

The town centre was scarred by some of the worst of the riots of summer 2011 when the destruction of the House of Reeves furniture store became an emblem of the outbreak of violent unrest. Several major retailers have closed in recent years, including department store Allders, which shut in September.

Last month another of the borough's biggest employers, travel insurance group Allianz Global Assistance, warned it may quit Croydon because of an exodus of middle-class residents.

The agreement between Westfield and Hammerson comes after months of negotiation with the Croydon Borough Council, the charitable Whitgift Foundation, which owns the freehold of the Whitgift Centre, and leaseholders.