Following David Cameron's announcement that there will be an in-out referendum on Britain's membership of the EU after the next general election, The Telegraph spoke to Professor Iain Begg of LSE who carried out the academic research that produced the figure that politicians have kept citing.
In research carried out with colleagues at South Bank University in 2000, they found that "three million jobs were associated with EU demand," Prof Begg said.
But he added that the figure was "not the same as saying that these jobs would disappear if we left the EU.
"Many of the jobs would still be sustained because people in other European countries would continue to buy some British goods," he added.
"So it's always been a bit of a false perspective to say that three million jobs would be lost.
"It wouldn't mean overnight losses of jobs. It wouldn't mean there would be a loss of prosperity instantly, just the risks become greater."