Angela Merkel warned last week that Europe may have to bring back internal border controls to cope with the worst refugee crisis since the Second World War. The German chancellor said she would prefer to retain the Schengen zone – which allows passport-free travel across most of mainland Europe – but that the system would collapse unless other countries agreed to accept their fair share of refugees. Germany expects to take in 800,000 asylum seekers this year, far more than any other EU member.