The number of EU migrants living in the UK has been undercounted by 250,000 over the past five years, an explosive report claims today.

The study said net migration from inside the EU was around 50,000 a year higher than official statistics admit.

Crucially, it would mean that migration from inside the EU – over which the Government has no control - is now higher than that from the rest of the world combined.

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The number of EU migrants living in the UK has been undercounted by 250,000 over the past five years, an explosive report claims today

Migrants and refugees cook near a fence at the northern Greek border point of Idomeni

Leave campaigners said it was now clear ministers had not been 'telling the truth' - and the numbers coming in from the EU were 'unsustainable'.

On Monday, Home Secretary Theresa May admitted EU membership makes it 'harder' to control immigration and that is not a 'good thing'.

The report comes after ministers spent months refusing to publish data which could reveal the full scale of EU immigration.

Migrationwatch compared net migration figures with population estimates for migrants born in the group of Eastern European countries including Poland and the Czech Republic, known as the EU8 nations.

Its report said: 'Between 2010 and 2015 the population born in the EU8 and living in the UK increased by an average of 90,000 a year but during the same period estimated net migration from the EU8 averaged only 40,000.

'This suggests that EU8 net migration has been undercounted by 50,000 a year in the last five years.'

Lord Green of Deddington, the chairman of Migration Watch said: 'This analysis casts serious doubt on the accuracy of our immigration figures.'

A row has been raging over the true scale of EU immigration since the Government refused Freedom of Information requests at the end of last year.

The study said net migration from inside the EU was around 50,000 a year higher than official statistics admit

Leave campaigners said it was now clear ministers had not been 'telling the truth' - and the numbers coming in from the EU were 'unsustainable'

Officially, 257,000 EU nationals were said to have arrived last year alone, but 630,000 people from the EU were given NI numbers

Figures from the Office for National Statistics - which are supposed to count people into the country - show some 919,000 EU migrants have arrived in Britain since June 2010.

But, in the same period of time, officials have issued 2.2 million NI numbers to EU migrants.

MPs say the gap suggests huge numbers of incomers may have been missed by the ONS – leaving officials in the dark about the true scale of the pressure being placed on hospitals and schools.

Brexit campaigners and economists have called for the release of the 'active' NI numbers, which means those which are currently being used to claim benefits or pay taxes.

They say this data will give a snapshot picture of who is actually here – and ensure the public are not voting in the referendum on the basis of inaccurate information on immigration.

After resisting for months, the HMRC agreed earlier this month to pass the information to the ONS. The ONS is now processing the information and plans to release it on May 26 – less than a month before the referendum.

Officially, 257,000 EU nationals were said to have arrived last year alone, but 630,000 people from the EU were given NI numbers.

The figures include 209,000 NI numbers given to Romanians and Bulgarians. Officially, only 55,000 Romanians and Bulgarians settled here last year.

209,000 NI numbers given to Romanians and Bulgarians but only 55,000 Romanians and Bulgarians settled here last year

In the latest official figures, overall international net migration was estimated at 323,000 for the year ending September - more than three times the government's aim of less than 100,000

A group of young migrants gather outside a tent at a makeshift camp at the northern Greek border point of Idomeni

Matthew Elliott, Chief Executive of Vote Leave said: 'The public should be told the facts when it comes to immigration and our borders so they can make an informed choice on 23 June.'

Tory MP Peter Bone, co-founder of Grassroots Out, said: 'It is time for the Government to own up about the true scale of EU immigration into this country.'

Steven Woolfe, UKIP's migration spokesman, said: 'To think that one third of a million, which is the current official net migration figure, looks likely to be a significant underestimate reinforces the scale of the problem.'S

In the latest official figures, overall international net migration was estimated at 323,000 for the year ending September - more than three times the government's aim of less than 100,000. But if Migration Watch are right, the true figure would be nearer 375,000.

Estimated net EU migration to the UK was 172,000 and 191,000 for non-EU migration, while 40,000 more Britons left the country than arrived.

A Home Office spokesperson said: 'It is absolutely essential that immigration statistics are robust and reliable, to inform government policy and be trusted by the public.

'That is why we continue to work closely with the ONS and support its work in providing an accurate understanding of all migration to and from the UK.'

*In a separate report, the National Institute of Economic and Social Research today claims that leaving the EU would have 'significant and damaging effects' on many British companies by restricting access to migrant workers.

The research claimed that the hospitality, food and drink and construction sectors were all concerned about their ability to fill vacancies if free movement of labour is reduced or comes to an end.