The general secretary of the GMB union Paul Kenny has blamed the Government after figures released by the House of Commons showed British workers' wages have suffered one of the sharpest falls in the European Union.
Mr Kenny said: "The Government is directly responsible for this unprecedented fall in the real value of wages in the three years since the election.
"Employers paying low wages get taxpayer subsidies in the form of tax credits to assemble a workforce for them to make decent profit margins."
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The Office for National Statistics said gross domestic product grew by just 0.1%.
William's comments came during a surprise appearance at an event scheduled for just his brother.
Matt Campbell, who collapsed just a few miles from the finish line, had hoped to raise £2,500.