I though Britain was was never part of EU... Germany was the most powerful nation in EU. They don't use Euro right?
The UK is part of the EU but not the Eurozone. The latter is an economic community with a common currency, the Euro. Britain still used the Pound-Sterling.
The EU has long been controversial in the UK. I remember seeing full page ads in British magazines in the early 2000s attacking the Eurozone. A lot of folks don't want Brussels dictating policy to Westminster. Which is understandable.
The two big issues right now the EU's economic situation, and immigration. The first deals with bankrupted states like Greece and Italy, whether they should be bailed out, and who's going to pay for it.
The immigration issue has been festering for a long time. However, it's recently got a big kick in the pants by the Syrian Civil War and Islamic State. Both refugees and extremists have been pouring across porous eastern borders. A lot of Muslim immigrants have failed to integrate. They've also made demands of European governments to implement things like Sharia Law. This is the exact reason why far right parties have been increasing in power and number over the last few years.
The UK is of course no stranger to violence by Islamic fundamentalists. There were the Muslim-Hindu riots in Bradford a number of years ago. The train bombings in 2005, the public beheading of a serviceman, accusations of extremism entering the schools, honour killings, female genital mutilation, etc. A lot of Brits feel resentful that this stuff has been allowed to go on. I can see why there's growing sentiment to close off the borders.