‘Experience has shown that fences and patrols at sea do not stop the refugees,’ he added.

Michael Gove said EU immigration policies were causing misery, with free movement diktats stopping the UK choosing who it wanted to let in. The Justice Secretary said this meant Britain could neither be ‘humane’ to refugees nor ‘wise’ economically.

EU leaders are now worried that tens of thousands of refugees are poised to start making their way through Europe via Romania, Ukraine and Poland. Donald Tusk, the president of the European Council, said the handling of the crisis had ‘key significance for the referendum campaign’.

Mr Leggeri, who heads the Frontex border agency, said: ‘It would be a success if the refugee numbers for this year remained stable in comparison to 2015. We are confronting a situation in Syria this year which will result in another million refugees.’

The latest net migration statistics due to be published by the ONS may beat the previous high of 336,000. The record was set for the year to June 2015. The latest figures will cover the 12-month period to the end of September last year. Some ministers fear that, for the first time, net migration from inside the EU may be higher than the figure for people who are from the rest of the world.

Last week it emerged the number of EU nationals working in the UK had rocketed by 215,000 in a single year. They included more than 120,000 Eastern Europeans, almost 50,000 of them Romanians and Bulgarians. Almost 1.2million Eastern Europeans now work in the UK. The total number of EU workers has rocketed by 840,000 to a record two million since Mr Cameron came to power on a pledge to curb mass migration.

Employment minister Priti Patel said: ‘Being a member of the EU has meant that the UK has lost control of its borders and its immigration policy. As a result of EU rules, the UK is open to 500million people from other EU member states who can live and work in the UK with no restrictions.

‘The mass influx of migrants from Eastern Europe in particular has contributed to pressures on the UK’s housing stock, public services and infrastructure.’

The Czech Republic’s prime minister yesterday warned that Britain leaving the EU would bring a wave of nationalism and separatism. ‘Rightist extremists and nationalists would open this theme sooner or later in the Czech Republic and other states,’ said Bohuslav Sobotka.