A top official at the Organisation for Economic Cooperation and Development (OECD) says the effects of Britain leaving the EU would be akin to a "tax" on British citizens.
In a speech at the London School of Economics on Wednesday, Secretary General Angel Gurria said: "Brexit would, rather like a tax, hit the wellbeing and the pockets of UK citizens.
"Unlike most taxes, however, this one will not finance the provision of public services or close the fiscal gap. The "Brexit tax" would be a pure deadweight loss, a cost incurred with no economic benefit. And this tax would not be a one-off levy. Britons would be paying it for many years."
The OECD is the latest in a growing line of major international institutions and figures putting their weight behind Britain remaining in the EU.
Earlier this month, the IMF said that Brexit could cause "severe regional and global damage" while last week, President Obama argued that the "UK is at its best when it's helping to lead a strong European Union. It leverages UK power to be part of the EU. I don't think the EU moderates British influence in the world, it magnifies it."
Secretary General Gurria spoke alongside the launch of a new OECD report, titled "The Economic Consequences of Brexit: A Taxing Decision"— which looks into the effects that could come if Britain were to choose to vote to leave the EU.
The report is a 35-page monster, filled with economic analysis and a whole heap of charts focusing on everything from trade impacts of Brexit, to how it would affect corporate bonds, and how GDP growth might react.
Here are some of the most important charts from the OECD's report — showing, it says, the benefits of Britain being in the EU, and the risks of Brexit — as well as analysis from the OECD.
"The risk of Brexit is increasingly reflected in financial asset prices. The cost of insuring UK public debt against sovereign default has been rising since 14 October, when the President of the European Commission first warned about only limited progress in negotiations with the UK. CDS spreads remain low relative to the financial crisis period, but their increase since mid-October is significant and higher than for peers."
"Uncertainty about the referendum has begun to hold back UK growth, and concerns are rising in European economies.
"Businesses have started to defer investment projects, with UK business investment declining by 2% in the last quarter of 2015. Some recent surveys of chief financial officers of the UK's largest companies indicate rising risk aversion, soaring uncertainty over business conditions, falling hiring decisions, and reduced capital spending intentions, with the UK's upcoming EU referendum considered to be the top risk to business prospects. Economic policy uncertainty has been growing over the recent months, more in the UK than in the EU, which has occurred in parallel to an easing in monthly estimates of UK GDP growth by the National Institute of Economic and Social Research."
It should be noted that earlier today, numerous economists argued that Brexit is not the only reason for slowing UK growth.
"The aftermath of a vote for leaving the EU would result in considerable additional volatility in financial markets and an extended period of uncertainty about future policy developments.
"Moreover, negotiations over UK withdrawal from the EU would need to take place over 2016-18, followed by trade negotiations with the EU in 2019-2023, which is likely to contribute to enhanced uncertainty for an extended period.
"Past experience indicates that greater uncertainty, whether reflected in the Economic Policy Uncertainty Index for the UK or greater stock market volatility, would be associated with higher corporate bond spreads."
"Brexit would generate a large negative shock to the UK economy, which would spillover to other European countries. Assuming fixed interest rates at the zero lower bound, UK GDP growth would be reduced by 0.5 percentage point in both 2017 and 2018.
"The onset of the trade shock in 2019 adds to these costs considerably, with GDP growth reduced by 1.5 percentage points that year. These shocks would be larger still without the depreciation of sterling included in the scenario, although the impact of such a change may be weaker now than in the past.
"By 2020, real GDP would be more than 3% below the level it would otherwise have been in the absence of Brexit, equivalent to a cost of GBP 2200 per household."
"The UK is the most attractive destination for FDI in the EU, partly owing to access to the EU internal market. The UK accounts for the largest share of FDI inflows into the EU. FDI positions in the UK of both EU and non-EU investors have steadily increased over time, and both groups cite the Single Market as fairly or very important for the UK's attractiveness for FDI, on top of its structural advantages, such as flexible labour and product markets. The large FDI inflows have contributed to greater trade integration of the UK with the EU and strengthened its comparative advantage in many sectors."
"The large current account deficit, which exposes the UK to a sudden stop, and debt refinancing issues are additional risks in the event of Brexit. The current account deficit was around 5.5% of GDP in the second half of 2015, and reached an unprecedented level of 7% of GDP in last quarter. It was financed significantly less by direct investment in the second half of the year (Figure 12, Panel B), creating important risks if there were to be sudden and large capital outflows."
"Immigrants, particularly from EU countries, have boosted GDP growth significantly in the UK. EU immigrants have higher employment rates than natives and almost all other migrant groups. Migrants from countries that acceded to the EU in 2004 (EU8 countries) have a higher employment rate than EU migrants in general.
"EU migrants also have a better education than in most other EU countries although wages of immigrants from EU8 countries are rather low. Immigration has been a key factor behind the strong labour market.
"After Brexit, immigration is likely to be restricted more significantly," the report adds.