Just less than 28% of registered Brits did not vote in the June EU referendum — that is about 13 million people.

Leave's margin of victory was 1,269,501 votes. It sounds a lot. But when you consider 13 million potential voters, for whatever reason, did not participate, you realise just how significant an increased turnout could have been.

At an event Business Insider attended on Wednesday morning, polling guru John Curtice presented research which suggests the majority of Brits who abstained in June would more than likely have backed Remain.

The chart below shows the results of a series of polls conducted after Britain voted for Brexit. Each pollster asked abstainers how they would vote if a second referendum was to take place, bar GQR, which asked them how they would have voted in the June referendum. The numbers speak for themselves:

The GQR poll is especially interesting. If 55% of the 13 million abstainers had gone to polling stations and backed Remain on the day, the campaign for Britain to stay in the EU would have received around 7.15 million extra votes.

Of course, this is just hypothetical. Plus, YouGov's research shown in the chart suggests the Remain-Leave gulf among abstainers was nowhere near as big as GQR found. But all the research shown below agrees on one basic theme — the Remain campaign failed to motivate potential supporters.

This was a concern for former prime minister David Cameron and the Remain campaign long before voting day. Business Insider noted two weeks before the referendum how every major pollster agreed that people who supported Brexit were more likely to actually vote than those who wanted Britain to remain the EU.

"It's true that abstainers were disproportionately more sympathetic towards Remain," Curtice said.

Britain's biggest pollsters may have struggled to predict the outcome of the referendum, but they were all correct in predicting that it would be difficult for the Remain campaign to persuade a sufficient amount of sympathisers to vote in its favour.