READ MORE HERE. The quotes:
"But legal and policy experts, as well as a senior British Government source, have admitted it would be "very difficult" to force those who are already here to take a dramatic cut in the benefits they receive even after the EU renegotiation. [...]
And Thom Brooks, professor of law at Durham University, said the measures "could only be taken against people who haven't arrived yet" [...]
Professor Brooks added: "The language surrounding this is very specific. If the UK wanted to pull the emergency brake it has to show some kind of objective consideration to EU migrants. They are going to need information about what EU migrants are doing and I can tell you, the Government does not have reliable statistics about the pressures of which nationalities are using the NHS and other things.
"You have to make an objective statement of facts and figures to Europe about EU migration pressures and they have to show it is EU migration that is causing the pressure and not non-EU migrants or it won't work, that's a problem for the Government." [...]