in a move that is likely to give British Prime Minister David Cameron a major headache.

The EU decides who's responsible for refugee based on something called the Dublin regulation,

which the European commission is set to scrap in March just as the Brexit campaign will be heating up.

But what do the rules say currently?

The law is pretty simple.

Refugee is supposed to apply for asylum in the first safe country they get to,

and that country is then responsible for processing the application.

If the refugee pops to be in a separate country having already applied for asylum in another,

he can quickly be sent back to the first country.

But what's going wrong with this?

The Dublin rule heats pressure on the countries on the EU's borders, especially Greece and Italy.

More than one million people have passed through the two countries in 2015 on their way to Northern Europe.

Brussels is set to scrap this "first country of entry" principle

and instead opt to share applications more evenly.

But why does this affect Britain?

The U.K. is allowed to pick-and-choose which EU migration rules it abides by

Britain has opted into the Dublin regulation partly because it allows them to deport asylum seekers

if they've been registered in another country.

This is an ability that the government is keen to keep.

But Brussels is likely to propose refugee sharing scheme in place of the current Dublin rules.

For David Cameron has a choice:

lose the ability to deport refugees easily,

potentially facing taking in extra,

or try to fight and find another special deal for Britain and Brussels.

In any case, the Prime Minister faces a tough few months.