The upsurge of migrants heading to Europe from Africa is threatening to undermine living standards and social structures in the EU, Foreign Secretary Philip Hammond has warned.
Mr Hammond said the continent could not absorb "millions" of Africans and that EU laws needed to be overhauled to ensure those coming simply to find a better way of life could be returned to their own country.
He said that in many cases, migrants knew they only had to set foot in Europe for there to be little chance of them ever being forced to leave.
"We have got to be able to resolve this problem ultimately by being able to return those who are not entitled to claim asylum back to their countries of origin. That's our number one priority," he told BBC News.
His comments came after Greek prime minister Alexis Tsipras warned that his country was being overwhelmed by the influx of arrivals crossing the Mediterranean from the Middle East and Africa.
Last month alone almost 50,000 migrants arrived in the EU through Greece compared to a total of 41,700 in the whole of last year, according to the latest figures from Frontex, the EU border agency.
Speaking during a visit to Singapore, Mr Hammond said the gap in living standards between Europe and Africa meant there would always be an "economic motivation" for Africans to try to make it to the EU.
"As long as the Europe Union's laws are the way they are, many of them will only have to set foot in Europe to be pretty confident that they will never be returned to their country of origin," he said.
"Now, that is not a sustainable situation because Europe can't protect itself and preserve its standard of living and social structure, if it has to absorb millions of migrants from Africa."
Mr Hammond said that ensuring migrants could be returned to their country of origin was also the key to resolving the "crisis" at Calais, where hundreds are gathered in the hope of being able to make it across the Channel to Britain.
"Having reviewed the situation in the light of the crisis it is clear that there is more that can be done to enhance the physical security of the tunnel," he said.
"But we also have to work with our French colleagues to try to deal with the root cause of the problem. So long as there are large numbers of pretty desperate migrants marauding around the area there will always be a threat to the tunnel's security."