If the United Kingdom votes to leave the European Union, the economies that face the biggest hit in the EU would be Ireland, the Netherlands, Belgium and Luxembourg, a Dutch study said on Thursday (9 June).

“There is a relatively large amount of trade between these countries and the UK, and they will be hit the hardest by the trade restrictions that would follow a Brexit,” said a report by the Netherlands Bureau for Economic Policy Analysis, an advisory institute of the ministry for economic affairs.

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Former PM's Blair and Major believe a Brexit could “tear apart the United Kingdom”. (Photo: sammydavisdog)

It calculated that, depending on the post-Brexit scenario, GDP in the Netherlands could fall between 0.9 percent to 2 percent.

Without a new free trade agreement to replace the current borderless trade between the UK and the Netherlands, the direct impact of a Brexit could cost around €575 per person in the Netherlands.

Under the assumption that trade leads to innovation and productivity, the per capita loss would be €1,000, the report said.

For the UK, the hit would be even harder without a new trade deal.

“The UK losses in 2030 ... would be around 4 percent of GDP. And, if we assume that innovation would lag behind due to reduced trade levels, these losses may even increase to nearly 9 percent of GDP.

“In that case, the UK losses would be similar to those experienced during the 2008–2009 crisis.”

The losses estimated by the Dutch study are significantly higher than Britain citizens themselves expect to suffer.

A survey published on Wednesday suggested undecided voters believed leaving the EU would leave them £71 (€90) worse off a year.

The reports were published two weeks before British citizens go to the polls, on 23 June.

It came as the Leave campaign criticised the UK government's decision to extend the deadline for registering to vote by 48 hours.

On Tuesday evening, the website where voters needed to register before being able to take part in the referendum crashed. On Wednesday, the government announced it would allow registrations until midnight on Thursday.

“They’ve just told the House of Commons that their website crashed last night because of the high demand, but we know that the government and their allies are trying to register as many likely Remain voters as possible,” Vote Leave campaigner Matthew Elliott said.

Meanwhile, the campaign continues.

Two former prime ministers are expected to hold a speech in Northern Ireland on Thursday, arguing for the UK to remain in the EU.

John Major, of the Conservative party, and his former rival Tony Blair, of Labour, will share a podium to say that leaving the EU could “tear apart the United Kingdom”.

“Not just a shrunken economy, not just a diminished United Kingdom on the world stage, but a smaller country in a very real and literal sense,” Major will say, according to a draft of the speech which was leaked to the British press.

“The most successful union in world history would be broken apart for good.”

There are fears that Scotland, generally more pro-EU than the rest of the UK, would want to have a second independence referendum if the UK leaves the EU without the Scots' consent.

And in Northern Ireland, the fragile peace between nationalists and unionists could come under strain if a land border with the Irish republic were to return, the prime ministers will say.