A third of Britons have experienced poverty in the past three years, and four million live in “persistent poverty,” research suggests. Cameron has presided over falling living standards, but says Brexit could make it worse.

Office for National Statistics (ONS) data says Britain has the 12th-highest "overall poverty" rate of the 28 countries in the EU, despite being the second-richest country after Germany.

The official measure of overall poverty is someone who has a disposable income 60 percent lower than the national average.

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But about 6.5 percent of the UK population, or 3.9 million people, have lived in “persistent poverty," defined as those who have experienced relative low income for at least the last three years.

That means the UK has the third-lowest persistent poverty rate in the EU, behind Denmark and the Czech Republic.

Romania, at 20 percent, has the highest rate of persistent poverty. Bulgaria is second on 16.5 percent and Lithuania third with 16 percent.

The persistent poverty rate in 2014 was 1.5 percent higher among women than men, and the likelihood of falling into poverty shoots up to 43 percent for those who leave education without any formal qualifications.

Prime Minister David Cameron, whose government has implemented a program of harsh austerity measures over the past six years, warns the poorest and most vulnerable people in the UK would be hit hardest by the economic consequences of leaving the EU.

He says leaving the EU would see prices rise and threaten jobs, while remaining in the union would help working people and British manufacturing.

Writing in the Daily Mirror, he said leaving would be a “national error.”

“I’ve been in this job for six years now. Whatever you think of me, I know how Britain gets things done in the world.

“I’ve seen how free trade within Europe benefits working people. I’ve seen how manufacturing is boosted by trade deals the EU has done with the rest of the world.”

He says three million people’s livelihoods are directly linked to trade with Europe, with “countless more” linked indirectly.

Cameron’s comments come as 306 business figures signed a letter backing Vote Leave.

The letter, published in the Daily Telegraph, says being a member of the EU undermines British competitiveness and that Brexit would create more jobs.