Half of retailers are considering decreasing staffing levels in the first quarter of 2013 compared with just a third at the same time last year.
New figures from retailers suggest more job losses are on their way after a decrease in footfall.
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Investigators believe Mr Kushner has significant information relevant to their inquiry, officials told NBC News.
The men were detained as part of an investigation by MI5 and the Metropolitan Police's Counter Terrorism Command.
As a minute's silence in honour of the Manchester bomb victims ended, a spontaneous singalong of Oasis' Don't Look Back in Anger broke out.