Mass migration is allowing terrorists to sneak into the EU, its own border agency admitted last night.

In a devastating report, it said the Paris attacks proved jihadists were exploiting the refugee crisis.

The Frontex agency logged a record 1.82 million illegal crossings into the EU last year – six times more than in 2014.

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Frontex logged a record 1.82 million illegal crossings into the European Union during 2015, as these failed asylum seekers from Afghanistan protest against their deportation today from the Greek island of Lesbos

Terrorists such as those behind last November's attack on Paris are using the chaos caused by the migrant crisis to sneak into Europe in order to commit atrocities and kill innocent civilians

Frontex said a large number of people arriving mainly in Greece and Italy with false documents are not facing thorough checks or penalties. Men and children are pictured in Idomeni on the Greek-Macedonian border

But it said it had no idea how many illegal migrants there were and, in any case, had no way of tracing their movements inside the EU.

Officials also warned a ‘staggering’ number of European citizens had become jihadists and were taking advantage of lax border controls.

‘The Paris attacks in November 2015 clearly demonstrated that irregular migratory flows could be used by terrorists to enter the EU,’ said the report, Frontex’s risk analysis for 2016. ‘With no thorough check or penalties in place for those making false declarations, there is a risk that some persons representing a security threat to the EU may be taking advantage of this situation.’

In another highly-charged day for the referendum debate:

EU judges ruled that foreign crime suspects cannot be deported automatically if they risk being imprisoned in degrading jail conditions abroad;

Cabinet minister Chris Grayling said the UK risks being left voiceless and subject to more harmful meddling by a ‘giant federation of eurozone states’;

The billionaire founder of Phones4U dismissed the prospect of huge job losses in the event of Brexit;

David Cameron insisted however it would be an ‘act of self-harm’ to quit the Brussels club;

Germany admitted that half of the one million refugees who have entered the country have vanished.

Dominic Raab, Tory justice minister, said: ‘This is a damning indictment by the very EU body charged with managing Europe’s external border.

‘Frontex has set out all too starkly the risks, including from crime and terrorism, that the EU’s free movement rules leave Britain wide open to.

‘With no solution in sight, the safer option is for Britain to leave the EU in order regain control over our borders and immigration policy.’

Frontex also revealed more than 1.8 million illegal border crossings were detected by EU member states in 2015, six times the number reported in 2014. Refugees from Afghanistan and Pakistan are pictured in Lesbos

Frontex warned that a 'staggering number of EU citizens' became jihadists in Syria before sneaking back into Europe hidden alongside refugees such as these photographed today on the Greek island of Lesbos

Two of those involved in the November 13 Paris attacks entered the EU through the Greek island of Leros and had been registered by the authorities after presenting fraudulent Syrian documents, Frontex said.

It added: ‘The staggering number of EU citizens who joined the (Syrian) conflict as jihadists has resulted in a number of returnees opting to use irregular means of travelling.

‘Islamist extremists will exploit irregular migration flows whenever such movements fit their plans.’ Frontex also pointed to the routes used for smuggling weapons, often traded from former conflict regions such as the Western Balkans.

Around 800,000 weapons are thought to be in illegal civilian possession in Bosnia and Herzegovina alone.

A few days before the Paris attack, German police officers discovered pistols, hand grenades, Kalashnikov rifles with ammunition and explosives.

Greek authorities have begun the process of deporting some failed asylum seekers to Turkey

Refugees facing deportation claim their lives will be at risk if they are sent back to Turkey

The weapons were transported from Montenegro to France in a car of a man probably linked to suspects behind the atrocity, Frontex said.

Syrian nationals accounted for the largest proportion of the 1.82million illegal entries – but still represented only one in three journeys. The share of Afghans rose toward the end of the year and Iraqis were the third largest nationality.

Many of the illegal crossings were by people who were counted for the first time when they arrived on the Greek islands from Turkey and again when they crossed one of the EU’s external borders in the Western Balkans. In all, more than one million people moved to Europe illegally in 2015 – the higher, 1.8million figure can be explained by multiple crossings by the same individuals.

Half a million refugees who poured into Germany over the past 18 months have failed to register with the authorities. The Federal Criminal Police office say this means they have either vanished into the black market or have plunged into the criminal underworld to get money because no registration means no benefits.

David Davis, a former Tory frontbencher, said: ‘The border of Syria is now at Calais because in effect there is no control and no knowledge of the whereabouts of a very large number of people.’ The revelations will reignite the debate over whether being inside the EU is a threat to Britain’s national security.

Lord Howard, a former Tory leader, has warned the Schengen open-border agreement is ‘like hanging a sign welcoming terrorists to Europe’.

Former MI6 chief Sir Richard Dearlove has also argued Britain could be safer outside the EU as it would be able to kick out more terrorists and control our own borders.