In an effort to win the 2015 election, Cameron promised an In-Out referendum on the issue by the end of 2017. The moment the date for it was announced, the rival campaigns began — not least the rival camps within the Conservative party, with ex-London Mayor Boris Johnson leading the "Leave" group and Cameron making the case for "Remain."
Thus, much of the campaigning has been a slug-out between Cameron and Johnson — the co-called blue-on-blue war — which has dominated the agenda and the media.
On the other hand, the Labour Party — led by lifelong Euroskeptic Jeremy Corbyn — is officially backing 'Remain' but has failed to engage with many voters and its own party membership — which a recent poll found was unsure of the party's official stance. Corbyn has been lukewarm in the campaign, drawing criticism from some of his parliamentarians.
The biggest issues for the mostly left-leaning, working class Labour supporters is immigration and the matter of foreign workers taking British jobs for less money and enjoying benefits. According to the latest poll by ORB, 44 percent of people who voted for Labour at the 2015 general election now back "Leave."
Now, former Labour Prime Minister Gordon Brown is stepping into the campaign in favor of remaining in the EU. He will argue that "smaller nations look to us for leadership. What message would we send to the rest of the world if we the British people — the most internationally minded of all — were to walk away from our nearest neighbors?"
His intervention brought derision on social media.
Cameron is hoping that the parliamentary Labour Party will urge Corbyn to take a stronger line on the UK remaining in the EU — despite his lifelong hatred of the EU — and that Brown's intervention will distract attention from his own party's blue-on-blue infighting as it tears itself apart over Europe.
With ten days to go and the polls looking perilously close, that's a big ask.