Imagine if you're from Maine and you move to California. Imagine that for some reason welfare/benefits are different in CA -- which in some cases they are.
Imagine there's a CA rule that you can only get the benefits you got in Maine, at the Maine dollar amount.
Imagine how that couldn't even be suggested, because of the rules that govern a federation such as the USA.
Now consider that the Conservative Party of Britain is proposing only giving benefits at the amount an "immigrant" (aka someone from somewhere else in Europe) could expect from their state of origin.
Imagine you are an intrinsically brilliant person from say Lithuania who can speak three languages fluently.
Imagine how this proposal makes you feel.
Britain, the Texas of Europe, busy sawing itself off the tree that allows it to think of itself as somewhat high up and covered in leaves.