Yep, pretty much this.
There's also a group in the UK that don't feel that the UK should take orders from the EU, but yeah, it's pretty much all about immigration.
Gronk, Citizens of the EU can travel to and work in any other country in the EU without the need of a Visa, and recently there have been more additions to the EU, with more smaller European countries joining, sparking fear in the UK that people from poorer European countries would flock to the UK looking for work (and taking jobs from Brittish people). The recent uptick in immigration of late has put a large strain on the UK's Public Health System and other Government funded programs, causing economic stress.
Leaving the EU means they can close this off, and ease the stress on these programs, at the same time being able to limit immigration.
It's an incredibly bad idea though, and has far worse implications that the brexit camp either aren't seeing or don't care about.
