The question is, do people from Romania and Bulgaria need a visa? Looks to me they can not just move to the UK but maybe the UK has different agreements with this countries.
Looks like they don't need anything but a passport to go to the UK.
That's because of the EU citizenship, which allows the free movement of people. Obtaining a work permit might be a different thing, but I'm really just guessing here...
No, Romanians can move to the UK for good with a Romanian ID. They don't need a passport. For those thinking about this now, it's decision time because as we now know, after March this won't be possible. 152,000 Romanians registered for UK National Insurance (NI) numbers in 2014/15