Ye olde Britain didn't wan't to be part of the EU anymore. People who wanted to leave cited the immigration problems running rampant in other EU member states, and that the EU was taking advantage of Britain or something or other, and people who wanted to stay wanted to stay because of fear of an economic collapse of British business and sterling.

How do they decide whether to remain or leave?

A vote called a referendum, where they decided if they wanted to opt out of the EU, or stay.

A fuck up every Brit will regret for years to come :)

The EU doesn't seem to think it's a fuck up. They're willing to give the Brits better renegotiation on trade deals and it seems that the EU is the one who wants Britain, not the other way around. When they can't disperse immigrants towards the UK, it'll blow up into a bigger problem they'll have to take steps to fix themselves, while the UK can handle their own situation without the EU stepping and choking any action they want to take.

Plus Germany is saying five other countries in the EU are looking for their own respective exits out of the EU. France, the Netherlands, Italy, Sweden, and Denmark populations are looking to follow in the UK's steps. they've clearly had enough of being told what to on the immigration issue, since the EU is content to do seemingly nothing on the issue.

Any British FS users that can share their view?