London - 27 April 2016

1. Wide of Angel Gurria, Secretary-General of the Organisation for Economic Co-operation and Development (OECD) speaking on stage at the Old Theatre, London School of Economics and Political Science (LSE)

2. Man taking photos

3. Close of audience

4. SOUNDBITE (English) Angel Gurria, Secretary-General, OECD:

"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."

5. Cutaway of audience

6. SOUNDBITE (English) Angel Gurria, Secretary-General, OECD:

"We estimate that in a Brexit scenario, GDP per household in 2030 would be lower than the baseline, that means staying, by at least 3,200 pounds and up to 5,000 pounds in the most pessimistic case."

7. Various of audience

8. SOUNDBITE (English) Angel Gurria, Secretary-General, OECD:

"While no one knows precisely what the costs would be, what is striking about our estimates and those produced by the other institutions, is that all the numbers under a Brexit case are negative. The best outcome under Brexit is still worse than remaining. And the worst outcomes are very bad indeed. Very expensive. The Brexit tax just gets bigger."

9. Wide of stage

10. Cutaway of economist Professor Lord Stern listening on stage

11. SOUNDBITE (English) Angel Gurria, Secretary-General, OECD:

"Our conclusion is unequivocal. The UK is much stronger as a part of Europe and Europe is much stronger with the UK as a driving force. There is no upside for the UK in Brexit. Only costs that can be avoided and advantages to be seized by remaining in Europe. No one should have to pay the Brexit tax."

12. Close of audience

13. Wide of stage

The head of the global economic forum OECD warned Britain that leaving the European Union would be tantamount to taxing its citizens - another in a growing cavalcade of cautionary advice ahead of a June 23 referendum on membership in the 28-nation bloc.

The warning by Angel Gurria, the secretary-general of the Organisation for Economic Co-operation and Development, came just days after expressions of concern by US President Barack Obama, the UK Treasury and the International Monetary Fund.

He described the notion that Britain might gain a better trade deal outside the union as somewhat fanciful.

Gurria's assessment follows that made by the UK Treasury last week, which determined that leaving the European Union would cost Britain the equivalent of 6,100 US dollars per household.

The estimate was based on an analysis of the long-term costs and benefits of EU membership and its alternatives.

The ever-more dire OECD judgment came the same day that authorities reported Britain's economy slowed in the first three months of the year amid concerns about the global economy as well as the vote on EU membership.

The UK economy grew by a quarter-on-quarter rate of 0.4 percent in January-March, down from 0.6 percent in the fourth quarter of last year, the Office for National Statistics said Wednesday.

Services, which comprise 78 percent of the British economy, continued to grow, expanding by 0.6 percent.

But other sectors declined, including construction, mining and manufacturing.