Britain has “the right” to control its borders, Theresa May will tell world leaders as she warns that hundreds of thousands of “economic migrants” are posing as refugees.

The Prime Minister will use a trip to the United Nations General Assembly this week to criticise the global response to “unmanaged migration”, warning that Western nations are simply “treating the symptoms of this crisis”.

Mrs May will say that “all countries” have a “responsibility” to manage their borders to reduce illegal and uncontrolled migration.

She will warn that the failure to differentiate between refugees and economic migrants is encouraging more people to pay criminal gangs to smuggle them into Europe where they can then attempt to claim asylum.