Ahead of the upcoming referendum, here's an animated history of the European UnionIBTimes UK

Nigel Farage has revealed his surprise that more celebrities have not come out for the 'Remain' campaign, after over 280 well-known figures signed a pro-EU letter. The stars, including author John le Carre, actress Keira Knightley and artist Tracey Emin, warned a Brexit would be "leap into the unknown" for millions of people across the UK.

"I'm very surprised there weren't more," the Ukip leader told journalists on 20 May. "If we go and knock on some doors of £500m houses in Notting Hill, I'm sure we'll find a few more." Some celebrities, such as acting legend Sir Michael Caine, have back a 'Leave' vote at the 23 June ballot.

But Farage suggested the A-list endorsements would have no impact on the referendum. "At the Scottish referendum the big celebrities made zero difference. I see the battle lines drawn as the people versus the political establishment," the Eurosceptic firebrand argued.

The Ukip leader made the comments as he launched his party's battle bus tour outside the European Parliament's offices in Westminster. The open-top vehicle will travel the "length and breadth" of Britain in the run-up to the referendum.

The event followed two major interventions in the campaign, with Canadian Prime Minister Justin Trudeau backing a 'Remain' vote and European Commission President Jean Claude Juncker warning the UK would be considered a "third-party state" by the EU after a Brexit.

"Project Fear will now move onto Project Threat, it sounds to me like Mr Juncker is playing that game," Farage said. "What else do you expect? His whole life has been dedicated to building up these anti-democratic structures in Brussels."

The Ukip leader also admitted he did not know what the result of the referendum would be. "I'm confident that those who have made their mind up and want to leave have a lot more passion than those who think we should remain," he claimed.

"This is about passion, after all it's about running your own country, it's about being a democracy [and] it's about being an independent nation. Who's going to win? I don't know – there's a huge discrepancy between online polls [and] telephone polls.

"There's a danger some people might get bored of this. At the end of the day it's a turnout referendum and if we can go and stir up as much interest as we can around the country, and have a bit of fun doing it at the same time, that would be a good thing."

The official Brexit campaign, Vote Leave, are running their own battle bus tour of the UK, with former Mayor of London Boris Johnson leading the campaign.

Nigel Farage shows his passport
Ukip leader Nigel Farage shows the media his passport as he launches a battle bus tour of the UK Ian Silvera/IBTimes UK